Portable drag compressor powered mechanical ventilator

ABSTRACT

A ventilator device and system comprising a rotating compressor, preferably a drag compressor, which, at the beginning of each inspiratory ventilation phase, is accelerated to a sufficient speed to deliver the desired inspiratory gas flow, and is subsequently stopped or decelerated to a basal flow level to permit the expiratory ventilation phase to occur. The ventilator device is small and light weight enough to be utilized in portable applications. The ventilator device is power efficient enough to operate for extended periods of time on internal or external batteries. Also provided is an oxygen blending apparatus which utilizes solenoid valves having specific orifice sizes for blending desired amounts of oxygen into the inspiratory gas flow. Also provided is an exhalation valve having an exhalation flow transducer which incorporates a radio frequency data base to provide an attendant controller with specific calibration information for the exhalation flow transducer.

FIELD OF THE INVENTION

[0001] The present invention pertains generally to medical equipment andmore particularly to a compressor powered mechanical ventilator devicefor delivering respiratory ventilation to a mammalian patient.

BACKGROUND OF THE INVENTION A. Principles of Mechanical Ventilation

[0002] In many clinical settings mechanical ventilators are used tofacilitate the respiratory flow of gas into and out of the lungs ofpatients who are sick, injured or anesthetized.

[0003] In general, mechanical ventilators provide a repetitive cyclingof ventilatory flow, each such repetitive cycle being separated into twophases—an inspiratory phase followed by an expiratory phase.

[0004] The inspiratory phase of the ventilator cycle is characterized bythe movement of positive-pressure inspiratory flow of gas through theventilator circuit and into the lungs of the patient. The expiratoryphase of the ventilatory cycle is characterized by cessation of thepositive pressure inspiratory flow long enough to allow lung deflationto occur. The exhaled gas is vented from the ventilator circuit,typically through an exhalation valve. In patient whose lungs andthoracic musculature exhibit normal compliance, the act of exhalation isusually permitted to occur spontaneously without mechanical assistancefrom the ventilator.

[0005] It is sometimes desirable to control the airway pressure duringexhalation to maintain a predetermined amount of positive back pressureduring all, or a portion of, the respiratory cycle. Such techniques areoften utilized to treat impairments of lung capacity due to pulmonaryatelectasis or other factors.

[0006] The mechanical ventilators of the prior art have been groupedunder various classification schemes, based on various criteria. Ingeneral, mechanical ventilators may be grouped or classified accordingto the parameter(s) which are utilized for a) triggering, b) limitingand c) terminating (e.g., cycling) the inspiratory phase of theventilator cycle.

[0007] “Triggering” is the action that initiates the inspiratory phaseof the ventilator cycle. The initiation of the inspiratory phase may betriggered by the ventilator or the patient. The variables and/orparameters which are utilized to trigger the beginning of theinspiratory phase include: time (i.e., respiratory rate), thecommencement of spontaneous inhalation by the patient and/orcombinations thereof.

[0008] “Limiting” of the inspiratory phase refers to the manner in whichthe inspiratory gas flow is maintained within prescribed ranges tooptimize the ventilation of the patient's lungs. The limiting variablesand/or parameters are typically controlled by the ventilator, but maychange as a result of patient effort and/or physiologic variables suchas lung compliance and airway resistance. The variables and/orparameters which are utilized for limiting the inspiratory phase includeflow rate, airway pressure and delivered volume.

[0009] “Terminating” or “cycling” of the inspiratory phase of theventilator cycle refers to the point at which the inspiratory flow isstopped and the ventilator and/or patient are permitted to “cycle” intothe expiratory phase. Depending on the ventilator control settings, thetermination of the inspiratory phase may be brought about by theventilator or the patient. The variables and/or parameters which areutilized to terminate the inspiratory phase include: time; peak airwaypressure; and/or tidal volume (V_(t)).

B. Mechanical Ventilation Modes Utilized in Modern Clinical Practice

[0010] In addition Mechanical ventilators are utilized to delivervarious “modes” of mechanical ventilation, the particular mode ofventilation being selected or prescribed based on the clinical conditionof the patient and the overall objective (i.e., long term ventilation,short term ventilation, weaning from ventilator, etc . . . ) of themechanical ventilation.

I. Ventilation Modes

[0011] i. Intermittent Mandatory Ventilation (IMV)

[0012] Intermittent Mandatory Ventilation is a ventilation mode whereina spontaneously breathing patient receives intermittent mechanicalinflation supplied asynchronously by the ventilator.

[0013] ii. Synchronized Intermittent Mandatory Ventilation (SMIV)

[0014] Synchronized Intermittent Mandatory Ventilation is a ventilationmode wherein a spontaneously breathing patient receives occasionalmandatory ventilatory breaths. Mandatory ventilator breaths aresynchronized with the patient's spontaneous inspiratory efforts.

[0015] iii. Controlled Mechanical Ventilation (CMV)

[0016] Controlled Mechanical Ventilation (CMV) is a ventilation modewherein mechanical breaths are delivered to the patient at timeintervals which are unaffected by patient efforts. Controlled MechanicalVentilation is typically utilized in patients who are not breathingspontaneously.

[0017] iv. Assist/Control Ventilation (A/C)

[0018] Assist/Control Ventilation (A/C) is a ventilation mode whereinthe patient is able to volitionally alter the frequency of mandatoryventilator breaths received, but can not alter the flow and title volume(V_(t)) of each ventilator breath received. Controlled, mandatorybreaths are initiated by the ventilator based on the set breath rate. Inaddition, the patient can demand and trigger an assist breath. Aftersuccessful triggering of an assist breath, the exhalation valve isclosed and gas is delivered to the patient to satisfy the preset tidalvolume, peak flow and wave form.

C. Breath Types Utilized in Modern Clinical Practice

[0019] Breath types are typically classified according to the particularfunctions which control:

[0020] a) triggering;

[0021] by) limiting; and

[0022] c) cycling of each breath delivered by the mechanical ventilator,as described and defined hereabove.

[0023] Typical breath types and ventilator parameters utilized in modernclinical practice include the following:

[0024] i. Machine-Cycled—Mandatory Breath

[0025] A machine-cycled, mandatory breath is a breath that is triggered,limited and cycled by the ventilator.

[0026] ii. Machine-Cycled—Assist Breath

[0027] A machine cycled assist breath is a breath that is triggered bythe patient, but is limited and cycled by the ventilator.

[0028] iii. Patient-Cycled—Supported Breath

[0029] A patient-cycled, supported breath is a breath that is triggeredby the patient, limited by the ventilator, and cycled by the patient.

[0030] iv. Patient-Cycled—Spontaneous Breath

[0031] A patient-cycled spontaneous breath is a breath that istriggered, limited and cycled by the patient. While patient effortlimits the flow, and hence the inspiratory volume of the breath, theventilator may also limit the breath by providing a flow that is to lowto maintain a constant pressure in the face of patient inspiratorydemand.

[0032] v. Volume-Controlled Mandatory Breaths

[0033] Volume-controlled breaths are machine-triggered mandatorybreaths. The inspiratory phase is initiated by the ventilatory based ona preset breath rate. The inspiratory phase is ended, and the expiratoryphase begun, when the breath delivery is determined to be complete basedon a preset tidal volume, peak flow and wave form setting. Theventilator remains in expiratory phase until the next inspiratory phasebegins.

[0034] vi. Volume-Controlled—Assist Breaths

[0035] Volume-controlled breaths are machine cycled supported breathsthat are initiated by the patient. Volume-controlled assist breaths maybe initiated only when the “assist window” is open. The “assist window”is the interval or time during which the ventilator is programmed tomonitor inspiratory flow for the purpose of detecting patientinspiratory effort. When a ventilator breath is triggered, theinspiratory phase of such breath will continue until a preset tidalvolume peak flow and wave form have been achieved. Thereafter, theexhalation valve is open to permit the expiratory phase to occur. Theventilatory remains in the expiratory phase until the nextpatient-triggered breath, or the next mandatory inspiratory phase,begins.

[0036] vii. Pressure-Controlled Breaths

[0037] Pressure-Controlled breaths are delivered by the ventilator usingpressure as the key variable for limiting of the inspiratory phase.During pressure control, both the target pressure and the inspiratorytime are set, and the tidal volume delivered by the ventilator is afunction of these pressure and time settings. The actual tidal volumedelivered in each pressure-controlled breath is strongly influenced bypatient physiology.

[0038] viii. Pressure Support Breaths

[0039] Pressure support breaths are triggered by the patient, limited bythe ventilator, and cycled by the patient. Thus, each breath istriggered by patient inspiratory effort, but once such triggering occursthe ventilator will assure that a predetermined airway pressure ismaintained through the inspiratory phase. The inspiratory phase ends,and the expiratory phase commences, when the patients inspiratory flowhas diminished to a preset baseline level.

[0040] ix. Sigh Breaths

[0041] A sigh breath is a machine-triggered and cycled,volume-controlled, mandatory breath, typically equal to 1.5 times thecurrent tidal volume setting. The inspiratory phase of each sigh breathdelivers a preset tidal volume and peak flow. The duration of theinspiratory phase of each sigh breath is limited to a maximum timeperiod; typically 5.5 seconds. The ventilator may be set to deliver asigh function automatically after a certain number of breaths or acertain time interval (typically 100 breaths for every 7 minutes), whichever interval is shorter. The sigh breath function it may be utilizedduring control, assist and SIMV modes of operation, and is typicallydisabled or not utilized in conjunction with pressure controlled breathtypes or continuous positive air way pressure (CPAP).

[0042] x. Proportional Assist Ventilation (PAV)

[0043] Proportional Assist Ventilation (PAV) is a type of ventilatorbreath wherein the ventilator simply amplifies the spontaneousinspiratory effort of the patient, while allowing the patient to remainin complete control of the tidal volume, time duration and flow patternof each breath received.

[0044] xi. Volume Assured Pressure Support (VAPS)

[0045] Volume Assured Pressure Support (VAPS) is a type of ventilatorbreath wherein breath initiation and delivery is similar to a pressuresupport breath. Additionally, the ventilator is programmed to ensurethat a preselected tidal volume (V_(t)) is delivered during suchspontaneously initiated breath.

D. Oxygen Enrichment of the Inspiratory Flow

[0046] It is sometimes desirable for mechanical ventilators to beequipped with an oxygen-air mixing apparatus for oxygen enrichment ofthe inspiratory flow. Normal room air has an oxygen content (FiO₂) of21%. In clinical practice, it is often times desirable to ventilatepatients with oxygen FiO₂ from 21% to 100%. Thus, it is desirable formechanical ventilators to incorporate systems for blending specificamounts of oxygen with ambient air to provide a prescribedoxygen-enriched FiO₂. Typically, volume-cycle ventilators which utilizea volume displacement apparatus have incorporated oxygen mixingmechanisms whereby compressed oxygen is combined with ambient air toproduce the selected FiO₂ as both gases are drawn into the displacementchamber during the expiratory phase of the ventilator cycle.Nonbellows-type volume-cycled ventilators have incorporated otherair-oxygen blending systems for mixing the desired relative volumes ofoxygen and air, and for delivering such oxygen-air mixture through theinspirations circuitry of the ventilator.

E. Regulation/Control of Expiratory Pressure

[0047] The prior art has included separately controllable exhalationvalves which may be preset to exert desired patterns or amounts ofexpiratory back pressure, when such back pressure is desired to preventatelectasis or to otherwise improve, the ventilation of the patient.

[0048] The following are examples of expiratory pressure modes which arefrequently utilized in clinical practice:

[0049] i. Continuous Positive Airway Pressure (CPAP)

[0050] Continuous Positive Airway Pressure (CPAP) is employed duringperiods of spontaneous breathing by the patient. This mode ofventilation is characterized by the maintenance of a continuouslypositive airway pressure during both the inspiratory phase, and theexpiratory phase, of the patient's spontaneous respiration cycle.

[0051] ii. Positive End Expiratory Pressure (PEEP)

[0052] In Positive End Expiratory Pressure a predetermined level ofpositive pressure is maintained in the airway at the end of theexpiratory phase of the cycle. Typically, this is accomplished bycontrolling the exhalation valve so that the exhalation valve may openonly until the circuit pressure has decreased to a preselected positivelevel, at which point the expiration valve closes again to maintain thepreselected positive end expiratory pressure (PEEP).

F. Portable Ventilators of the Prior Art

[0053] The prior art has included some non-complex portable ventilatorswhich have inherent limitations as to the number and type of variablesand/or parameters which may be utilized to trigger, limit and/orterminate the ventilator cycle. Although such non-complex ventilators ofthe prior art are often sufficiently power efficient and small enoughfor portable use, their functional limitations typically render themunsuitable for long term ventilation or delivery of complex ventilationmodes and or breath types.

[0054] The prior art has also included non-portable, complexmicroprocessor controlled ventilators of the type commonly used inhospital intensive care units. Such ventilators typically incorporate amicrocomputer controller which is capable of being programmed to utilizevarious different variables and/or parameters for triggering, limitingand terminating the inspiratory phase of the ventilator cycle. Complexventilators of this type are typically capable of delivering manydifferent ventilation modes and or breath types and are selectivelyoperable in various volume-cycled, pressure cycled or time-cycled modes.However, these complex ventilators of the prior art have typically beentoo large in size, and too power inefficient, for battery-drivenportable use. As a result of these factors, most of the complexmicro-processor controlled ventilators of the prior art are feasible foruse only in hospital critical care units.

[0055] As is well known there exist numerous settings, outside ofhospital critical care units, where patients could benefit from theavailability of a small, battery powered, complex microprocessorcontrolled mechanical ventilator capable of delivering extended modes ofventilation. For example, critically ill patients sometimes requiretransport outside of the hospital in various transport vehicles, such asambulances and helicopters. Also, critical care patients are sometimestransiently moved, within the hospital, from the critical care unit tovarious special procedure areas (e.g., radiology department, emergencyroom, catheterization lab etc.,) where they may undergo diagnostic ortherapeutic procedures not available in the critical care unit.Additionally, patients who require long term ventilation are not alwayscandidates for admission to acute care hospital critical care units ormay be discharged to step-down units or extended care facilities. Also,some non-hospitalized patients may require continuous or intermittentventilatory support. Many of these patients could benefit from the useof complex microprocessor controlled ventilators, but may be unable toobtain such benefit due to the non-feasibility of employing suchventilators outside of the hospital-critical care unit environment.

[0056] In view of the foregoing limitations on the usability of priorart complex microprocessor controlled volume-cycled ventilators, thereexists a substantial need in the art for the development of a portable,highly efficient, ventilator capable of programmed delivery of variousmodern ventilatory modes and breath types, while also being capable ofuse outside of the hospital critical care unit environment, such as intransport vehicles, extended care facilities and patients homes, etc.

[0057] U.S. Pat. No. 4,493,614 (Chu et al.) entitled “PUMP FOR APORTABLE VENTILATOR” describes a reciprocating piston pump which ispurportedly usable in a portable ventilator operable on only internal orexternal battery power.

[0058] U.S. Pat. No. 4,957,107 (Sipin) entitled “GAS DELIVERY MEANS”describes a rotating drag compressor gas delivery system which isostensibly small enough to be utilized in a portable ventilator. Thesystem described in U.S. Pat. No. 4,957,107 utilizes a high speed rotarycompressor which delivers a substantially constant flow of compressedgas. The rotary compressor does not accelerate and decelerate at thebeginning and end of each inspiratory phase of the ventilator cycle.Rather, the rotating compressor runs continuously, and a diverter valueis utilized to alternately direct the outflow of the compressor a) intothe patients lungs during the inspiratory phase of the ventilationcycle, and b) through an exhaust pathway during the expiratory phase ofthe ventilation cycle.

[0059] Thus, there remains a substantial need for the development of animproved portable mechanical ventilator which incorporates the followingfeatures:

[0060] A. Capable of operating for extended periods (i.e., at least 2½hours) using a single portable battery or battery pack as the sole powersource;

[0061] B. Programmable for use in various different ventilatory modes,such as the above-described IMV, SMV, CMV, PAV, A/C and VPAS.

[0062] C. Usable to ventilate non-intubated mask patients as well asintubated patients.

[0063] D. Oxygen blending capability for delivering oxygen-enrichedinspiratory flow.

[0064] E. Capable of providing controlled exhalation back pressure forCPAP or PEEP.

[0065] F. Portable, e.g., less than 30 lbs.

SUMMARY OF THE INVENTION

[0066] The present invention specifically addresses the above referenceddeficiencies and needs of the prior art by providing comprises amechanical ventilator device which incorporates a rotary compressor fordelivering intermittent inspiratory gas flow by repeatedly acceleratingand decelerating the compression rotor at the beginning and end of eachinspiratory-phase. Prior to commencement of each inspiratory ventilationphase, the rotary compressor is stopped, or rotated at a basalrotational speed. Upon commencement of an inspiratory phase, the rotarycompressor is accelerated to a greater velocity for delivering thedesired inspiratory gas flow. At the end of each inspiratory phase, therotational velocity of the compressor is decelerated to the basalvelocity, or is stopped until commencement of the next inspiratoryventilation phase. A programmable controller is preferably incorporatedto control the timing and rotational velocity of the compressor.Additionally, the controller may be programmed to cause the compressorto operate in various modes of ventilation, and various breath types, asemployed in modern clinical practice.

[0067] Further in accordance with the present invention, there isprovided an oxygen blending apparatus which may be utilized optionallywith the rotatable compressor ventilation device of the presentinvention. The oxygen blending apparatus of the present inventioncomprises a series of valves having flow restricting orifices of varyingsize. The valves are individually opened and closed to provide a desiredoxygen enrichment of the inspiratory gas flow. The oxygen blendingapparatus of the present invention may be controlled by a programmablecontroller associated with, or separate from, the ventilator controller.

[0068] Still further in accordance with the invention, there is providedan exhalation valve apparatus comprising a housing which defines anexpiratory flow path therethrough and a valving system for controllingthe airway pressure during the expiratory phase of the ventilationcycle. A pressure transducer monitors airway pressure during exhalationthe output of which is used by the controller to adjust the valvingsystem to maintain desired airway pressure.

[0069] In addition the present invention utilizes an exhalation flowtransducer to accurately measure patient exhalation flow which may beutilized for determination of exhaled volume and desired triggering ofinspiratory flow. In the preferred embodiment, the exhalation flowtransducer is integrally formed with the exhalation valve, however,those skilled in the art will recognize that the same can be a separatecomponent insertable into the system. To insure transducer performanceaccuracy, in the preferred embodiment, the particular operationalcharacteristics of each flow transducer are stored within a memorydevice preferably a radio-frequency transponder mounted within theexhalation valve to transmit the specific calibration information forthe exhalation flow transducer to the controller. Further, theparticular construction and mounting of the flow transducer within theexhalation valve is specifically designed to minimize fabricationinaccuracies.

[0070] Further objects and advantages of the invention will becomeapparent to those skilled in the art upon reading and understanding ofthe following detailed description of preferred embodiments, and uponconsideration of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0071]FIG. 1 is a basic schematic diagram of a preferred ventilatorsystem of the present invention incorporating, a) a rotary compressorventilator device, b) an optional air-oxygen blending apparatus; and c)a controllable exhalation valve, and d) a programmable controller orcentral processing unit (CPU) which is operative to control andcoordinate the functioning of the ventilator, oxygen blending apparatusand exhalation valve.

[0072]FIG. 2 is a detailed schematic diagram of a ventilator system ofthe present invention.

[0073]FIG. 3 is a front view of the control panel of a preferredventilator system of the present invention.

[0074]FIG. 4 is a perspective view of a preferred drag compressorapparatus which may be incorporated into the ventilator system of thepresent invention.

[0075]FIG. 5 is a longitudinal sectional view through line 5-5 of FIG.4.

[0076]FIG. 6 is an enlarged view of a segment of FIG. 5.

[0077]FIG. 7 is an enlarged view of a segment of FIG. 6.

[0078]FIG. 8 is an elevational view of a preferred drag compressorcomponent of a mechanical ventilator device of the present invention.

[0079]FIG. 9 is a perspective view of the drag compressor component ofFIG. 8.

[0080]FIG. 10 is an enlarged view of a segment of FIG. 9.

[0081]FIG. 11a is a longitudinal sectional view of a preferredexhalation valve of the present invention.

[0082]FIG. 11b is a perspective view of the preferred spider bobbincomponent of the exhalation valve shown in FIG. 11a.

[0083]FIG. 11c is an exploded perspective view of a portion of theexhalation valve of FIG. 11a.

[0084]FIG. 11d is a perspective view of a portion of the exhalationvalve shown in FIG. 11c.

[0085]FIG. 11e is an exploded perspective view of the preferred flowrestricting flapper component of the exhalation valve shown in FIGS.11a-11 d.

[0086]FIG. 12 is a graphic example of flow vs. speed vs. pressure datagenerated for a preferred exhalation valve of the present invention,accompanied by an exhalation valve characterization algorithm computedtherefrom.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0087] The following detailed description and the accompanying drawingsare provided for purposes of describing and illustrating a presentlypreferred embodiment of the invention and are not intended to describeall embodiments in which the invention may be reduced to practice.Accordingly, the following detailed description and the accompanyingdrawings are not to be construed as limitations on the scope of theappended claims.

A. General Description of the Preferred Ventilator System

[0088] With reference to FIGS. 1-2, the mechanical ventilation system 10of the present invention generally comprises a) a programmablemicroprocessor controller 12, b) a ventilator device 14, c) an optionaloxygen blending apparatus 16 and d) an exhalation valve apparatus 18.Which is preferably implemented as a portable, battery powered system.

[0089] The ventilator device 14 incorporates a rotating drag compressor30 which is driven by an electric motor 102. In response to controlsignals received from controller 12, a bladed rotor within thecompressor 30 will undergo rotation for specifically controlled periodsof time and/or, within specifically controlled parameters, so as toprovide inspiratory gas flow through line 22 to the patient PT.

[0090] The controller 12 comprises a programmable microprocessor whichis electrically interfaced a) to the ventilator device 14 by way ofcontrol line 13, b) to the optional oxygen blending apparatus 16 by wayof control line 17, and c) to the exhalation valve 18 by way of controlline 19 and also by RF communication between flow transducer transponder(21) and transmitter/receiver (23). Preferably incorporated into theexhalation valve 18 as will be described in more detail infra.

[0091] The controller 12 is preferably programmed to utilize selectedparameters (e.g., time, flow rate, tidal volume (V_(t)), airwaypressure, spontaneous breath initiation, etc.) for triggering, limitingand cycling the inspiratory flow in accordance with the selectedventilatory mode or breath type.

[0092] At the end of each inspiratory flow cycle, the patient PT ispermitted to exhale through exhalation valve 18. The flow rate orpressure of the expiratory flow through exhalation valve 18 iscontrolled by varying the degree of flow restriction within theexhalation valve 18, in response to control signals received throughline 19 from controller 12. This enables the exhalation valve 18 to beutilized to create a selected expiratory back pressure (e.g., CPAP,PEEP).

[0093] Optional oxygen blending apparatus 16 may be utilized to enrichthe oxygen content of the inspiratory gas flow provided by the dragcompressor ventilator device 14. The preferred oxygen blending apparatus16 comprises a plurality of (preferably five (5)) solenoid valves 52,each having a specific sized flow restricting orifice. The solenoidvalves 52 are arranged in parallel between an oxygen inflow manifold 26and an oxygen outflow manifold 28. The controller 12 is programmed toopen and close the individual solenoid valves 52 for specific periods oftime so as to provide a metered flow of oxygen through oxygen outflowmanifold 28 and into accumulator 54. Ambient air is drawn throughconduit 24 and filter 50, into accumulator 54, where the ambient aircombines with the metered inflow of oxygen to provide an oxygen-enrichedinspiratory flow containing a prescribed oxygen concentration (FIO₂).

[0094] The presently preferred embodiment of the system 10 will operatewhen supplied with voltage input within the range of 85-264 VAC at 50/60Hz.

[0095] An AC power cord is preferably connectable to the system 10 toprovide AC power input.

[0096] Additionally, the system 10 preferably includes an internalbattery capable of providing at least 15 minutes, and preferably 30minutes, of operation. During internal battery operation, somenon-essential displays may be dimmed or disabled by the controller 12.The internal battery is preferably capable of being recharged by ACpower input provided through the AC power cable, or by a separatebattery charger. The internal battery is preferably capable of beingfully charged, from a no charged state, within 24 hours. The internalbattery charge light 306 shown on the panel of the preferred controller12 a may additionally flash if desired during charging of the internalbattery.

[0097] Also, the system may include an external battery or battery setcapable of providing at least 2 hours of operation, and preferablycapable of providing 4 to 8 hours of operation. During external batteryuse, some non-essential displays may be dimmed or disabled by thecontroller 12. The battery or battery set is preferably capable of beingrecharged by delivery of AC power through the AC power cable, or by aseparate battery charger. It is preferable that the external battery orbattery set be capable of being fully charged, from a no charged statewithin 24 to 48 hours. The external battery charge light 310 on thepanel of the preferred controller 12 a may additionally flash if desiredduring charging of the external battery or battery set.

B. The Preferred Controller Apparatus

[0098] It will be appreciated that the controller 12 of the ventilatorsystem 10 of the present invention will vary in complexity, depending onthe specific capabilities of the system 10, and whether or not theoptional oxygen blending apparatus 16 is incorporated.

[0099]FIG. 3 shows the control panel of a preferred controller apparatus12 a which is usable in connection with a relatively complex embodimentof the ventilatory system 10, incorporating the optional oxygen blendingapparatus 16.

[0100] Controls Settings and Displays

[0101] The specific control settings and displays which are included inthe preferred controller 12 a, and the ways in which the preferredcontroller 12 a receives and utilizes operator input of specific controlsettings, are described herebelow:

[0102] 1. Standby-Off Control

[0103] The ventilator system 10 incorporates a stand by/off switch (notshown) which turns the main power on or off. A group of indicator lights300 are provided on the face panel of the controller 12 a, and are morefully described herebelow under the heading “monitors”. In general, thepanel indicator lights include an “on” indicator 302 which becomesilluminated when the ventilator is turned on. An AC power low/failindicator light 304 activates when the AC power cord is present and thevoltage is out of a specified operating range. Upon sensing low orfaulty AC power, the controller 12 a will automatically switch theventilator 14 to internal battery power. The ventilator will continue tooperate on internal battery power until such time as power in theinternal battery reaches a minimum level. When the power in the internalbattery reaches a minimum level, the controller 12 a will cause theinternal battery light and/or audible alarm 308 to signal that theinternal battery is near depletion.

[0104] A separate external battery light and/or audible alarm 312 isalso provided. The external battery light and/or audible alarm willactivate when the external battery is in use, and has a battery voltagewhich is out of the acceptable operation range. During this condition,the controller 12 a will cause all nonessential displays and indicatorsto shut down.

[0105] When AC power is connected to the ventilator 14, but theventilator is turned off, any internal or external batteries connectedto the ventilator will be charged by the incoming AC current. Internalbattery charge indicator light 306 and external battery charge indicatorlight 306 and external battery charged indicator light 310 are provided,and will blink or otherwise indicate charging of the batteries when suchcondition exists.

[0106] 2. Mode Select

[0107] A mode select module 320 incorporates plural, preferably five (5)mode select buttons 322, 324, 326, 328, 330. Mode select button 322 setsthe system 10 for Assist Control (a/c). Mode select button 324 sets thesystem 10 for Synchronized Intermittent Mandatory Ventilation (SIV).Mode select button 326 sets the system for Continuous Positive AirwayPressure (CPAP).

[0108] Spare mode select buttons 328, 330 are provided to permit thecontroller 12 a to be programmed for additional specific ventilationmodes such as volume assured pressure support (VAPS) or proportionalassist ventilation. When the controller is programmed for additionalspecific ventilation modes, select buttons 328, 330 may becorrespondingly labeled and utilized to set the ventilator 14 to deliversuch subsequently programmed ventilation modes.

[0109] 3. Tidal Volume

[0110] A digital tidal volume display 332, with corresponding tidalvolume setting button 332 a are provided. When tidal volume settingbutton 332 a is depressed, value setting knob 300 may be utilized todial in a selected tidal volume. The tidal volume display 332 will thenprovide a digital display of the currently selected tidal volume value.

[0111] The typical range of setable tidal volumes is 25 ml-2000 ml.

[0112] 4. Breath Rate

[0113] A digital breath rate display 334, with corresponding breath ratesetting button 334 a is provided. When breath rate setting button 334 ais depressed, value setting knob 300 may be utilized to dial in thedesired breath rate. Breath rate display 334 will thereafter display thecurrently selected breath rate.

[0114] The typical rage of selectable breath rates is 0 to 80 breathsper minute.

[0115] 5. Peak Flow

[0116] A digital peak flow display 336, and corresponding peak flowsetting button 336 a are provided. When peak flow setting button 336 ais depressed, value setting knob 300 may be utilized to dial in thedesired peak flow. The peak flow display 336 will, thereafter, provide adigital display of the currently selected peak flow.

[0117] The typical range of peak flow settings is 10 to 140 liters perminute.

[0118] 6. Flow Sensitivity

[0119] A flow sensitivity digital display 338, and corresponding flowsensitivity setting button 338 a are provided. When flow sensitivitysetting button 338 a is depressed, value setting knob 300 may beutilized to dial in the desired flow sensitivity setting. The flowsensitivity setting display 338 will, thereafter, provide a digitaldisplay of the currently selected flow sensitivity setting.

[0120] The flow sensitivity setting determines the trigger level forinitiation of volume and pressure-controlled assist breaths or pressuresupport breaths. The initiation of volitional inspiratory effort by thepatient creates a change in airway flow as determined by: (turbine biasflow)−(exhalation flow)=patient flow. Triggering occurs when the patientairway flow exceeds the sensitivity setting. The typical range ofselectable flow sensitivity settings is from one to ten liters perminute, or off.

[0121] Optionally, a fail safe feature may be incorporated whereby, ifthe patients flow demand does not exceed the flow sensitivity setting,but the airway pressure drops more than 5 cmH₂O below the set PEEPlevel, and inspiratory cycle will be initiated and a breath will bedelivered based on current mode and control settings.

[0122] 7. PEEP/CPAP

[0123] A PEEP/CPAP digital display 340, with corresponding PEEP/CPAPsetting button 340 a are provided. When PEEP/CPAP setting button 340 ais depressed, the value setting knob 300 may be utilized to dial in thedesired PEEP/CPAP setting.

[0124] The current PEEP/CPAP setting sets the level of pressure in thepatient circuit that is maintained between the end of inspiration andthe start of the next inspiration. It is also known as the “baseline”pressure.

[0125] The preferred range of PEEP/CPAP setting is 0 to 50 cmH₂O.

[0126] 8. Pressure Support

[0127] A pressure support digital display 342, and correspondingpressure support setting button 342 a, are provided. When pressuresupport setting button 142 a is depressed, value setting knob 300 may beutilized to dial in the desired pressure support setting.

[0128] The pressure support setting determines the inspiratory patientcircuit pressure during a pressure support breath. This control sets thepressure support level above the baseline setting established by thePEEP/CPAP setting. The total delivered pressure equals the PEEP or CPAPvalue+pressure support.

[0129] The typical range of pressure support settings is from 1 to 60centimeters of water (cmH₂O), or off.

[0130] 9. FiO₂(%O₂)

[0131] An FiO₂ digital display 348, and corresponding FiO₂ settingbutton 348 a, are provided. When the FiO₂ setting button 348 a isdepressed, the value setting knob 300 may be utilized to dial in thedesired fractional percentage of oxygen in the air/oxygen gas mixturethat is delivered to the patient PT and used for the bias flow. Inresponse to the FiO₂ setting, the controller 12 will issue controlsignals to the oxygen blending apparatus 16 to effect the preset FiO₂.

[0132] The preferred range of setable FiO₂ is between 0.21 and 1.0(i.e., 21-100 percent oxygen)

[0133] 10. Pressure Control (Optional)

[0134] A pressure control digital display 350, and correspondingpressure control setting button 350 a are provided. When the pressurecontrol setting button 350 a is depressed, the value setting knob 300may be utilized to dial in the desired pressure control value.

[0135] The pressure control setting enables the system 10 to be utilizedfor pressure control ventilation, and determines the inspiratorypressure level during delivery of each pressure control breath. Thepressure control setting sets the pressure level above any PEEP.

[0136] It is preferable that the range of possible pressure controlsettings be from 1 to 100 cmH₂O.

[0137] 11. Inspiratory Time (Optional)

[0138] An optional inspiratory time digital display 352, andcorresponding inspiratory time setting button 352 a may be provided.When the inspiratory time setting button 352 a is depressed, the valuesetting of 300 may be utilized to dial in the desired inspiratory time.

[0139] The set inspiratory time is the time period for the inspiratoryphase of a pressure control breath. Thus, this inspiratory time settingis normally usable for pressure control ventilation.

[0140] It is preferable that the range of setable inspiratory timesbeing from 0.3 to 10.0 seconds.

[0141] 12. Additional Displays/Settings

[0142] Additional digital displays 344, 346, 354, 356 and correspondingsetting buttons 344 a, 346 a, 354 a, 356 a are provided to permit thecontroller 12 to be subsequently programmed or expanded to receive anddisplay additional control settings beyond those which have beendescribed hereabove.

[0143] 13. Sigh On/Off

[0144] A sigh on/off button 360 is provided. When sigh on/off button 360is depressed, the controller 12 will cause the ventilator 14 to delivera sigh breath. A sigh breath is a volume-controlled, mandatory breaththat is usually equal to 1.5 times the current tidal volume settingshown on tidal volume setting display 332. The sigh breath is deliveredaccording to the current peak flow setting shown on peak flow settingdisplay 336. The inspiratory phase of the sigh breath is preferablylimited to a maximum of 5.5 seconds. During a sigh breath, the breathperiod is automatically increased by a factor of 1.5. The sigh breathfunction is available during all ventilation modes.

[0145] A single depression of the sigh on/off button 348 will cause theventilator to deliver a volume-controlled sigh breath once every 100breaths or every 7 minutes, which ever comes first. The sigh breathbutton 360 includes a visual indicator light 360 a which illuminateswhen the sigh on/off button 360 is depressed and the sigh/breathfunction is active.

[0146] 14. Manual Breath

[0147] A manual breath button 362 is also provided. Upon depression ofthe manual breath button 362, the controller 12 will cause theventilator 14 to deliver a single volume-controlled or pressure controlbreath in accordance with the associated volume and/or pressure controlsettings. An indicator light 362 a will illuminate briefly when manualbreath button 362 is depressed.

[0148] 15. Remote Alarm (Optional)

[0149] A remote alarm on/off control button 364 is provided to enable ordisable the remote alarm. When the remote alarm on/off control button364 is depressed, indicator light 364 a will illuminate. When the remotealarm on/off button 364 is depressed, the remote alarm will be enabled.When this function is enabled, alarm conditions will transmit via hardwire or radio frequency (wireless) to a remote alarm which may bemounted on the outside of a patients room so as to signal attendantsoutside of the room, when an alarm condition exists.

[0150] The specific alarm conditions which may be utilized with theremote alarm function, are described in greater detail herebelow.

[0151] 16. Flow Waveform (Optional-Applies to Volume Breaths Only)

[0152] The controller 12 includes a square flow wave form activationbutton 366 and a decelerating taper flow wave form actuation button 368.When the square flow wave form actuation button 366 is depressed,indicator light 366 a will illuminate, and the ventilator will deliverinspiratory flow at a constant rate according to the peak flow setting,as input and shown on peak flow display 336. When the decelerating paperwave form actuation button 368 is depressed, indicator light 368 a willilluminate, and the ventilator will deliver an inspiratory flow whichinitially increases to the peak flow setting, as input and shown on peakflow display 336, then such inspiratory flow will decelerate to 50percent of the peak flow setting at the end of the inspiratory phase.

[0153] 17. Inspiratory Hold (Optional)

[0154] An inspiratory hold actuation button 370 is provided, to enablethe operator to hold the patient at an elevated pressure followinginspiration, so that breath mechanics can be calculated. The length ofthe delay period is determined by the period of time during which theinspiratory hold button 370 remains depressed, with a maximum limitapplied.

[0155] 18. Expiratory Hold (Optional)

[0156] The controller 12 also includes an expiratory hold actuationbutton 372, which enables the ventilator to calculate auto PEEP. Duringthe expiratory hold, the turbine 30 operation is halted and theexhalation valve 18 remains closed. The difference between the endexpiratory pressure, as measured at the end of the expiratory holdperiod, minus the airway pressure reading recorded at the beginning ofthe expiratory hold period, will be displayed on monitor window 384.

[0157] 19. Maximal Inspiratory Pressure/Negative Inspiration Force(Optional)

[0158] The preferred controller 12 also incorporates a maximalinspiratory pressure test button 374, to enable the operator to initiatea maximal inspiratory pressure (MIP) test maneuver. This maneuver causesthe ventilator to stop all flow to or from the patient. The patientinspiratory effort is then monitored and displayed as MIP/NIF in themonitor window 384.

[0159] 20. 100% O₂ Suction (Optional)

[0160] Optionally, the controller 12 a includes a 100% O₂ actuationbutton 376 which, when depressed, will cause indicator light 376 a toilluminate and will cause the system 10 to deliver an FiO₂ of 1.00(i.e., 100% oxygen) to the patient for a period of three (3) minutesregardless of the current FiO₂ setting and/or breath type setting.

[0161] This 100% O₂ feature enables the operator to selectively deliver100% oxygen to the patient PT for a three minute period tohyperoxygenate the patient PT prior to disconnection of the patient fromthe ventilator circuit for purposes of suctioning, or for other clinicalreasons.

[0162] 21. Additional Control Actuation Buttons

[0163] An additional control actuation button 378, with indicator light378 a, is provided to enable the controller 12 a to be subsequentlyprogrammed to perform additional control actuation functions beyondthose described hereabove.

[0164] Monitors and Indicators

[0165] 1. AC Power Status Indicator

[0166] An AC power indicator light 304 is provided in the face panel ofthe controller 12 to indicate when sufficient AC power is available andthe standby/off switch (not shown) is in the standby position.

[0167] 2. Internal Battery Status Indicator(s)

[0168] An internal battery status indicator light 308 is provided on thepanel of the controller 12, and will indicate battery charge levelaccording to predetermined color signals. A separate internal batterycharge indicator light 306 may be provided, and will indicate chargingstatus according to predetermined color signals.

[0169] 3. External Battery Status Indicator(s)

[0170] An external battery status indicator light 312 is provided on thepanel of the controller 12, and will indicate battery charge levelaccording to predetermined color signals. A separate external batterycharge indicator light 310 may be provided, and will indicate chargingstatus according to predetermined color signals.

[0171] 4. Airway Pressure Monitor

[0172] The display panel of the controller 12 includes a real timeairway pressure bar graph display 380. A green indicator bar will appearon the airway pressure bar graph display 380 to indicate the real timeairway pressure at all times. Red indicators will appear on the airwaypressure bar graph to indicate high and low peak pressure alarm setting,as more fully described herebelow under the heading “Alarms”. An ambercolored indicator will appear on the airway pressure bar graph display380 to indicate the current PEEP/CPAP setting, Pressure Support settingand/or Pressure Control setting. A patient effort indicator light 382 islocated near the airway pressure bar graph display 380, and willilluminate to indicate the occurrence of a patient-initiated breath,including all spontaneous, assist or pressure support breaths.

[0173] 5. Digital Monitor Display

[0174] The panel of the controller 12 preferably includes a digitalmonitor display 384 and an accompanying monitor select button 386. Thecontroller 12 is programmed to display various monitored parameters.Each time the monitor select button 386 is depressed, the monitoredparameters displayed on monitor display 384 will change. The individualparameters may include: exhaled tidal volume, i.e., ratio, mean airwaypressure, PEEP, peak inspiratory pressure, total breath rate, totalminute ventilation.

[0175] Additionally, a display power saving feature may be incorporated,whereby the controller 12 will automatically cause the monitor display384 to become non-illuminated after a predetermined display period whenthe system 10 is operating solely on internal or external battery power.Each time the monitor select button 386 is depressed, the display 384will illuminate for a predetermined period of time only, and then willbecome non-illuminated. This feature will-enable the system 10 toconserve power when the system 10 is being operated solely on internalor external battery power.

[0176] Additionally, the controller 12 may be programmed to cause themonitor display 384 to display a special or different group ofparameters during a specific operator-initiated maneuver. Examples ofspecial parameter groups which may be displayed during a specificmaneuver include the following:

[0177] Real-time Pressure (at start of and during all maneuvers)

[0178] Plateau Pressure (Inspiratory Hold)

[0179] Compliance (Inspiratory Hold)

[0180] End Expiratory Pressure (Expiratory Hold)

[0181] Auto PEEP (Expiratory Hold)

[0182] Maximal Inspiratory Pressure (MIP/NIF)

[0183] Alarms and Limits

[0184] The preferred controller 12 may be programmed to receivedoperator input of one or more limiting parameters, and to provideaudible and/or visual alarm indications when such limiting parametershave been, or are about to be, exceeded.

[0185] The visual alarm indicators may comprise steady and or flashinglights which appear on the control panel of the preferred controller 12a.

[0186] The audible alarm components will preferably comprise electronicbuzzers or beepers which will emit sound discernable by the human earfor a preselected period (e.g., 3 seconds). Preferably, the audibleportion of any alarm may be volitionally muted or deactuated by theoperator.

[0187] Additionally it is preferable that the controller 12 beprogrammed to automatically reset each alarm if the current ventilationconditions do not fall outside of the preset alarm limits.

[0188] Examples of specific limiting parameters and alarm limits whichmay be programmed into the preferred controller 12, are as follows:

[0189] 1. High Peak Pressure

[0190] The preferred controller 12 includes, on its face panel, a highpressure digital display 390 and a corresponding high pressure alarmlimit setting button 390 a. When the high pressure alarm limit settingbutton 390 a is depressed, value setting knob 300 may be utilized todial in a desired high pressure alarm limit value. Such high pressurealarm limit value will then be displayed on high pressure alarm limitdisplay 390.

[0191] The currently set high pressure alarm limit, as shown on highpressure alarm limit display 390, will establish the maximum peakinspiratory pressure for all breath types. When the monitored airwaypressure exceeds the currently set high pressure alarm limit, audibleand visual alarms will be actuated by the controller 12 and thecontroller will immediately cause the system 10 to cycle to expiratorymode, thereby allowing the airway pressure to return to the baselinebias flow level and along the exhalation valve 18 to regulate pressureat any currently-set peep level.

[0192] In order to avoid triggering of the high pressure alarm duringdelivery of a sigh breath, the controller 12 will be programmed toautomatically adjust the high pressure alarm limit value by a factor of1.5× during the deliver of a sigh breath, provided that such does notresult in the high pressure limit value exceeding 140 cmH₂O. Thecontroller 12 is preferably programmed not to exceed a high pressurelimit setting of 140 cmH₂O, even during delivery of a sigh breath.

[0193] 2. Low Peak Pressure

[0194] A low peak airway pressure limit display 392, and correspondinglow peak pressure limit setting button 392 a, are also provided. Whenthe low peak pressure limit setting button 392 a is depressed, valuesetting knob 300 may be utilized to dial in a desired low peak airwaypressure alarm limit value. Such low peak pressure alarm limit valuewill then be displayed in the low peak pressure display 392.

[0195] Audible and/or visual alarms will be activated if the monitoredairway pressure fails to exceed the low peak pressure alarm limitsetting during the inspiratory phase of a machine-cycled mandatory orassist breath.

[0196] The controller 12 is preferably preprogrammed to

[0197] 5. Spare Alarm Limit Displays and Setting Buttons

[0198] Spare alarm limit displays 396, 398, and corresponding sparealarm limit setting buttons 396 a and 398 a are provided, to permit thecontroller 12 to be subsequently expanded or programmed to receiveoperator input of additional limiting parameters, and to provideauditory and/or visual alarms when such limiting parameters have beenexceeded.

[0199] 6. Ventilator Inoperative

[0200] A separate ventilator inoperative light indicator 400 is providedon the face panel of the controller 12. The controller 12 is programmedto cause the ventilator inoperative light to illuminate whenpredetermined “ventilatory inoperative” conditions exist.

[0201] 7. AC Power Low/Fail

[0202] The controller 12 is preferably programmed to activate visualand/or auditory alarms when an AC power cord is connected to the system10 and the voltage received by the system 10 is outside of a specifiedoperating range. The controller 12 is preferably also programmed toautomatically switch the system 10 to internal battery power under thiscondition. The AC power low/fail alarm can be silenced, and will remainsilenced, until such time as the internal low battery alarm 208 becomesactuated, indicating that the internal battery has become depleted.

[0203] 8. External/Internal Battery Low/Fail

[0204] The controller 12 may be programmed to actuate a visual and orauditory alarm when an external or internal battery is in use, and thebattery voltage is outside of an acceptable operating range.

[0205] 9. O₂ Inlet Pressure

[0206] The controller 12 may be programmed to provide auditory and/orvisual alarms when the oxygen pressure delivered to the system 10 isabove or below predetermined limits.

[0207] 10. Over Pressure Relief Limit

[0208] The system 10 includes a mechanical variable pressure reliefvalve 64, to relieve any over pressurization of the patient circuit.

[0209] The range of setable over pressure relief limit values may bebetween 0 to 140 cmH₂O.

[0210] Self Testing and Auto Calibration Functions

[0211] 1. Self Test Function

[0212] The preferred controller 12 may be programmed to perform aself-testing function each time the ventilator is powered up. Such selftesting function will preferably verify proper functioning of internalcomponents such as microprocessors, memory, transducers and pneumaticcontrol circuits. Such self testing function will also preferably verifythat electronic sub-systems are functioning correctly, and are capableof detecting error conditions relating to microprocessor electronics.

[0213] Also, during power up, the controller 12 may be programmed toallow a qualified operator who enters a given key sequence, to accesstrouble shooting and calibration information. In accordance with thisfeature, the key operator may induce the controller to display, on themonitor display 384, information such as the following:

Software Revision Peak Flow and Pressure Transducer Output Lamp Test/AllDisplays on Any Auto Zero and Purge Functions for the Flow PressureTransducer Event Detection Menu Including Previous Status or Fault CodesRemote Alarm Test and Program; and Data Communications Test and Program

[0214] Also, the controller 12 may be-programmed to allow a qualifiedoperator who entered a given key sequence, to access a user preferenceand set up menu. Such menu may include a monitory display 384, ofinformation such as the following:

[0215] System lock, enable or disable;

[0216] Variable Apnea interval;

[0217] Language selection; and

[0218] User verification tests.

[0219] The user preference and set up menu function may also beaccessible during operation of the system 10.

C. A Preferred Rotary Drag Compressor Apparatus

[0220] The portable system 10 ventilator of the present inventionpreferably incorporates a rotary drag compressor apparatus 30 comprisinga dual-sided, multi-bladed rotor 104 disposed within a rigid compressorhousing 106. An inflow/outflow manifold 108 is formed integrally withthe compressor housing 106, and incorporates two (2) inflow passageways112 and two (2) outflow passageways 110 for channeling gas flow into andout of the compressor apparatus 30.

[0221] An electric motor 102, such as a 0.8 peak horsepower, 40 voltD.C. motor, is preferably mounted integrally within the compressorhousing 106. Alternatively, the motor 102 may be encased or housed in anencasement or housing which is separate from the compressor housing 106.The motor shaft 114 extends transversely into, a bore 116 formed in thecentral hub 118 of rotor 104. As shown, the bore 116 of the central hub118 of rotor 104 may include a rectangular key-way 121 formed on oneside thereof and the motor shaft 114 may include a correspondingelongate rectangular lug formed thereon. The rectangular lug of themotor shaft 114 inserts within and frictionally engages the key-way 121of the rotor hub 118, thereby preventing the motor shaft 114 fromrotationally slipping or turning within the bore 116 of the rotor hub118. It will be appreciated however, that various alternative mountingstructures, other than the lug and keyway 121 shown in FIGS. 8-9, may beutilized to rotatably mount the motor shaft 114 to the rotor 104.

[0222] The rotor hub 118 is preferably formed having a concaveconfiguration, as shown in FIG. 5. Such concave configuration serves toimpart structural integrity and strength to the rotor 104, withoutsignificantly increasing the mass of the rotor 104 as would result fromthe formation of additional strengthening ribs or bosses on the rotorhub 118.

[0223] As shown in FIGS. 5-10, a first annular trough 120 extends aboutthe periphery of the front side of the rotor 104, and a second annulartrough 122 extends about the periphery of the backside of the rotor 104.

[0224] A multiplicity of rotor blade-receiving slots 126 are formedangularly, at evenly spaced intervals about the inner surfaces of thefirst 120 and second 122 annular troughs. Rotor blades 128 are mountedat spaced-apart locations around each annular trough 120, 122 such thatthe radial peripheral edge 127 of each blade 128 is inserted into andresides within a corresponding blade receiving slot 126 and the leadingedge 129 of each blade traverses across the open annular trough 120 or122, as shown. Each blade 128 is affixed by adhesive, or other suitablemeans, to the body of the rotor 104.

[0225] In the preferred embodiment the blades 128 are located in axiallyaligned positions, i.e., non-staggered directly opposite positions onopposite sides of the rotor 104 so as to promote even pressure balanceand symmetrical weight distribution within the rotor 104.

[0226] The rotor 104 is rotatably mounted within the compressor housing106 such that the first 120 and second 122 annular cavities are inalignment with the inflow 110 and outflow 112 channels, as shown.

[0227] In order to optimize the controllability of the rotor 104velocity, and to minimize the wear or stress on the system drivecomponents from repeated abrupt starting and stopping of the rotor 104,it is desirable that the overall mass of the rotor 104 be minimized.Toward this end, the body of the rotor 104 is preferably constructed oflight weight material such as aluminum, and the individual blades 128 ofthe rotor 104 are preferably constructed of light weight material suchas glass-filled epoxy. In embodiments where the body of the rotor 104 isformed of aluminum and the blades 128 are formed of glass-filled epoxy,a suitable adhesive such as epoxy may be utilized to bond the radialedges of the blades 128 within their corresponding blade-receiving slots126. Alternatively, it is contemplated to form the rotor and bladesintegrally, as by way of a molding process whereby metal (e.g.,aluminum), polymer or composite materials are molded to form the blades128 and rotor 104 as a unitary structure.

[0228] After the rotor blades 128 have been mounted and secured in theirrespective blade-receiving slots 126, each individual blade 128 willpreferably be disposed at an angle of attack A, relative to a flattransverse plane TP projected-transversely through the body of the rotor104, between the first annular trough 120 on the front side of the rotor104, and the second annular trough 122 on the backside of the rotor 104.The angle A is preferably in the range of 30-60 degrees and, in thepreferred embodiment shown in FIGS. 8-10 is 55 degrees. Such angle A isselected to provide optimal flow-generating efficiency of the rotor 104.

[0229] In operation, it is necessary to precisely control the timing ofthe acceleration, deceleration, and the rotational speed, of the rotor104 in order to generate a prescribed inspiratory pressure and/or flowrate and/or volume. Although standard manufacturing tolerances may bemaintained when manufacturing the rotor 104 and other components of thecompressor 30 (e.g., the rotor 104, compressor housing 106, motor 102)each individual compressor 30 will typically exhibit some individualvariation of flow output as a function of the rotational speed anddifferential pressure of that compressor 30. Thus, in order to optimizethe precision with which the inspiratory flow may be controlled, it isdesirable to obtain precise flow and pressure data at various turbinespeeds for each individual compressor 30, and to provide suchcharacterization data to the controller 12 to enable the controller 12to adjust for individual variations in the pressure and/or flow createdby the particular compressor 30 in use. As a practical matter, this maybe accomplished in either of two ways. One way is to generate discreteflow rate, speed and pressure measurements for each compressor 30 at thetime of manufacture, and to provide a table of such discreet flow rate,speed and pressure values to the ventilator controller 12 at the timethe particular compressor 30 is installed. The controller 12 will becorrespondingly programmed to perform the necessary interpolativemathematical steps to obtain instantaneous flow, speed or pressuredeterminations as a function of any two such variables, for theparticular compressor 30. The second way is to experimentally generate aseries of flow, speed and pressure data points over a range of normaloperating rotor speeds, and to subsequently derive a unique speed vs.flow vs. pressure equation to characterize each individual compressor30. Such individual characterization equation is then programmed into,or otherwise provided to, the controller 12 and the controller 12 isprogrammed to utilize such equation to compute precise, instantaneousspeed, flow rate and pressure control signals for controlling theindividual compressor 30 in use. An example of such graphical speed vs.flow rate vs. pressure data, and a characterization equation derivedtherefrom, is shown in FIG. 12.

[0230] Given the current cost of microprocessor technology, providing acontroller 12 which has the capability to receive and process such acharacterization equation as shown in (FIG. 12) for controlling thecompressor 30 would require substantial expense and size enlargement ofthe controller 12. Accordingly, given the present state of the art, itis most desirable to utilize the former of the two above-describedmethods—that is, providing a database of discrete flow, speed andpressure values and programming of the controller 12 to perform thenecessary mathematical interpolations of the provided data points formaintaining compressor-specific control of the pressure, flow rateand/or volume of gas provided in each inspiratory phase at theventilation cycle. The experimentally generated database of discreetflow, speed and pressure valves may be encoded onto an EPROM or anyother suitable database storage device. Such EPROM or other databasestorage device may be located on or within the compressor 30 itself andcommunicated to the controller 12 via appropriate circuitry.Alternatively, such EPROM or database storage device may be installeddirectly into the controller 12 at the time the particular compressor 30is installed within the ventilator device 14.

[0231] The controlled inspiratory flow generated by the rotary dragcompressor 30, exists from the compressor outlet 34 and through line 22to the patient PT. As shown in FIG. 2, an output silencer 60, such as ahollow chamber having a quantity of muffling material formedtherearound, is preferably positioned on inspiratory flow line 22 toreduce the sound generated by the ventilator 14 during operation. Aninspiration occlusion valve 62 is additionally preferably mounted oninspiratory flow line 22 to accomplish operator controlled stoppage ofthe inspiratory flow as required during performance of a maximalinspiratory force maneuver. Additionally, a pressure relief valve 64 isconnected to inspiratory flow line 22 to provide a safeguard againstdelivering excessive inspiratory pressure to the patient PT. Thepressure relief valve 64 may be manually set to the desired limitpressure, by the operator.

[0232] In general, the rotary drag compressor ventilator 14 operates byperiodic rotating of the rotor 130 within the compressor 30 to generatethe desired inspiratory gas flow through line 22. It is desirable thatthe rotor 130 be accelerated and decelerated as rapidly as possible.Such rapid acceleration/deceleration is facilitated by a reduction ininertial effects as a result of the above-described low massconstruction of the rotor 104. The speed and time of rotation of therotor 104, during each inspiratory phase of the ventilator cycle, iscontrolled by the controller 12 based on the variables and/or parameterswhich have been selected for triggering, limiting and terminating theinspiratory phase.

[0233] The precise flow, volume or pressure delivered through theinspiratory line 22 is controlled by the controller based on theEPROM-stored compressor characterization data received by thecontroller, as well as periodic or continuous monitoring of therotational speed of the rotor 104 and the change in pressure (Δ_(P))between the inlet side 32 and outlet side 34 of the compressor 30 asmonitored by the differential pressure transducer 36.

[0234] In the presently preferred embodiment, the controller 12 isprogrammed to deliver breaths by either of two available closed loopalgorithms; volume or pressure.

EXAMPLE Volume Breaths

[0235] Prior to Volume breath initiation, the controller 12 generates apredefined command waveform of flow vs time. The waveform is generatedusing the current Flow, Volume and Waveform input settings from thefront panel. Since the mathematical integral of flow over time is equalto the volume delivered, the controller can determine the appropriateinspiratory time. Once a volume breath has been triggered, thecontroller uses closed loop control techniques well known in the art todrive the compressor, periodically read the compressor differentialpressure and rotational speed, and then calls upon the specific storedcompressor characterization data to arrive at the actual flow rate. Onceactual flow rate is known, it is compared or “fed back” to the currentcommanded flow, and a resulting error is derived. The error is thenprocessed through a control algorithm, and the compressor speed isadjusted accordingly to deliver the desired flow rate.

[0236] This process is repeated continuously until the inspiration iscomplete.

EXAMPLE Pressure Breaths

[0237] Pressure breaths include several breath types such as PressureSupport or Pressure Control. In these breath types, the controllercommands the compressor to provide flow as required to achieve apressure as input from the front panel. Once a pressure breath has beentriggered, the controller uses closed loop, control techniques wellknown in the art to drive the compressor 30 and to achieve the desiredpatient airway pressure. The controller periodically reads the actualairway pressure. Once actual pressure is known, it is “fed back” andcompared to the current commanded pressure, and a resulting error isderived. The error is then processed through a control algorithm, andthe compressor speed is adjusted accordingly to deliver the desiredpressure. This process is repeated continuously until the inspiration iscomplete.

[0238] For both breath types, once the selected inspiratory terminationvariable is reached, the controller will signal the compressor motor 102to stop or decelerate to a baseline level, thereby cycling theventilator in to the expiratory phase.

D. A Preferred Oxygen Blending Apparatus

[0239] When oxygen enrichment of the inspiratory flow is desired, thecontroller 12 may be additionally programmed or equipped to control theoperation of the oxygen blending apparatus 16 to mix a prescribed amountof oxygen with ambient air drawn through air intake 24, therebyproviding an inspiratory flow having a prescribed oxygen content (FiO₂)between 21% -100%.

[0240] As shown in FIGS. 2 and 3, the preferred oxygen blendingapparatus 16 comprises an air inlet line 24 which opens into a hollowvessel or accumulator 54.

[0241] Oxygen inlet line 26 is connected to a pressurized source ofoxygen and leads, via a manifold to a series of solenoid valves 52.Although not by way of limitation, in the preferred embodiment as shownin FIG. 3, five (5) separate solenoid valves 52 a-52 e are utilized.Each such separate solenoid valve 52 a-52 e has a specific (usuallydiffering) sized flow restricting orifice formed therein so that eachsuch solenoid valve 52 a-52 e will permit differing amounts of oxygen topass into accumulator 54, per unit of time during which each suchsolenoid valve 52 a-52 e is maintained in an open position. Thecontroller 12 is preprogrammed to determine the specific period(s) oftime each solenoid valve 52 a-52 e must remain open to provide thenecessary amount of oxygen to accumulator 54 to result in the prescribedoxygen concentration (FiO₂).

[0242] Algorithm for a Preferred Oxygen Blending Apparatus

[0243] The rotational velocity of the rotor 104 and differentialpressure across the inflow/outflow manifold 108 are measured by thecontroller 12 and from this data the controller 12 is able to determinethe flow of gas through the compressor 30 from the accumulator 54. Thecontroller 12 integrates the air flow drawn through the compressor 30 todetermine the accumulated volume of enriched gas drawn from saidaccumulator 54. In order to maintain the flow of gas at the prescribedFiO₂ level, a portion of this removed volume must be replaced in theaccumulator 54 with pure oxygen.

[0244] The accumulated volume is compared to a predetermined triggervolume for each of the solenoids 52 a-52 e, which in the preferredembodiment, is defined by the equation:

Trigger Volume=(Solenoid Flow*Time*79)/[(FiO²⁻²¹)*2]

[0245] Starting with the smallest, each solenoid that is not currentlyopen is compared. When the accumulated volume reaches the trigger volumefor a solenoid 52, the controller 12 opens that solenoid 52 for a periodof time allowing oxygen to flow from the oxygen inlet line 26 throughthe solenoid 52 and into the accumulator 54. The controller 12 thenadjusts the accumulated volume appropriately by subtracting a volume,proportional to the volume of oxygen delivered to the accumulator 54from the accumulated volume defined by the equation:

Subtracted Volume=(Solenoid Flow*Time*79)/(FiO₂-21).

[0246] This process is repeated continuously.

[0247] The trigger volume the controller 12 uses to open an individualsolenoid 52 a-52 e is independent for each solenoid 52 and is functionof the flow capacity of the particular solenoid 52 a-52 e, theprescribed FiO₂ level, and the amount of time the solenoid 52 is open.In the preferred embodiment, the amount of time each solenoid 52 is openis the same for each solenoid 52, but may vary as a function of oxygeninlet pressure.

EXAMPLE Delivery of 0.6 FiO₂ Using 4 Solenoids

[0248] In this example, the oxygen blending apparatus has 4 solenoidswith flows of 5 lpm, 15 lpm, 40 lpm, and 80 lpm respectively. The FiO₂setting is 60%, thus the trigger volumes for each of the 4 solenoids is8 ml, 25 ml, 66 ml, and 133 ml respectively. Furthermore a constantoxygen inlet pressure is assumed resulting in an “on” time of 100 ms forthe solenoids, a constant compressor flow of 60 lpm, and a period of 1ms. The following table describes the state of the oxygen blendingalgorithm after various iterations: Solenoid Solenoid Solenoid SolenoidAccumulated 1 2 3 4 Time (ms) Volume (ml) (8 ml) (25 ml) (66 ml) (133ml)  0 0 off off off off  1 1 off off off off  2 2 off off off off **  77 off off off off  8 0 on off off off  9 1 on off off off **  32 24 offoff off off  33 0 on on off off  34 1 on on off off **  98 65 on on offoff  99 0 on on on off 100 1 on on on off ** 107 8 on on on off 108 1off > on* on on off

[0249] Thus, by independently operating the four (4) separate solenoidsas shown in the above table, a 0.6 FiO₂ is consistently deliveredthrough the compressor 30.

E. A Preferred Exhalation Valve and Exhalation Flow Transducer

[0250] Referring generally to FIGS. 11a-11 e the preferred exhalationvalve and exhalation flow transducer assembly of the present inventionis depicted. By way of overview, the exhalation valve 18 comprises ahousing which defines an expiratory flow path therethrough and a valvingsystem for controlling the airway pressure during the expiratory phaseof the ventilation cycle. The exhalation valve 18 shares numerousstructural and functional attributes with the exhalation valve describedin U.S. Pat. No. 5,127,400 (DeVries et al) entitled VentilatorExhalation Valve, issued Jul. 7, 1994, the disclosure of which isexpressly incorporated herein by reference.

[0251] In addition, the exhalation valve assembly 18 of the presentinvention additionally incorporates an exhalation flow transducer 230which serves to monitor exhalation flow from the patient and generatesan output signal to the controller 12. The output signal is thenutilized by the controller to determine when patient exhalation hasceased to thereby initiate inspiratory flow to the patient. In thepreferred embodiment, the exhalation flow transducer 230 is mountedwithin the exhalation valve 18 in unique structure to minimizemanufacturing inaccuracies. Further, in the preferred embodiment, theparticular operational characteristics of the exhalation flow transducer230 are stored within a memory device which is then communicated to thecontroller 12 to insure accuracy in flow measurements. The exhalationflow transducer 230 of the present invention shares numerous structuraland functional attributes with the flow transducer described in the U.S.Pat. No. 4,993,269, issued to Guillaume et al., entitled VariableOrifice Flow Sensing Apparatus, issued on Feb. 19, 1991, the disclosureof which is expressly incorporated herein by reference.

[0252] Referring more particularly to FIGS. 11a through 11 e, theexhalation valve 18 of the present invention is formed having a housing200 including an exhalation tubing connector 202 formed at a firstlocation thereon and an outflow port 204 formed at a second locationthereon. An exhalation gas flow passageway 206 extends through theinterior of the housing 200 such that expiratory gas may flow from theexhalation tubing connector 202 through the exhalation passageway 206within the interior of the exhalation valve 18 and subsequently passedout of the outflow port 204. Midway through the expiratory flowpassageway 206, there is formed an annular valve seat 208. The annularvalve seat 208 may be disposed in a plane which is parallel to the planeof the flat diaphragm 210 or alternatively, as in the embodiment shown,the annular valve seat 208 may be slightly angled or tapered relative tothe plane in which the flat diaphragm 210 is positioned. Such angling ortapering of the valve seat 208 facilitates seating of the diaphragm 210on the valve seat 208 without flutter or bouncing of the diaphragm 210.The elastomeric disc or diaphragm 210 is configured and constructed toinitially contact the farthest extending side of the angled valve seat208, and to subsequently settle or conform onto the remainder of theangled valve seat 208, thereby avoiding the potential for flutter orbouncing which may occur when the diaphragm 210 seats against a flatnon-angled valve seat 208.

[0253] The disc or diaphragm, 210 is preferably attached to thesurrounding rigid housing 200 by way of an annular flexible frenulum212. Frenulum 212 serves to hold the disc or diaphragm 210 in axialalignment with the annular valve seat 208, while permitting the disc ordiaphragm 210 to alternatively move back and forth between a closedposition wherein the diaphragm 210 is firmly seated against the valveseat 208 (FIG. 11a) and a fully open position wherein the disc ordiaphragm 210 is retracted rearwardly into the adjacent cavity withinthe housing 200 thereby providing an unrestricted flow path 206 throughwhich expiratory gas may flow.

[0254] A pressure distributing plate 214 is mounted on the backside ofthe diaphragm 210. A hollow actuation shaft 216 is mounted within thehousing 200 and is axially reciprocal back and forth to control theposition of the diaphragm 210 relative the valve seat 208. A bulbous tipmember 218 is mounted on the distal end of a hollow actuation shaft 216.A corresponding pressure distribution plate 214 is mounted on the backof the diaphragm 210. Forward movement of the actuation shaft 216 causesthe bulbous tip member 218 to exert forward pressure against the plate214 thereby forcing the diaphragm 210 toward its closed position. Whenthe actuation shaft 216 is in a fully forward position, the diaphragm210 will be held in firm abutment against the annular valve seat 208thereby terminating flow through the passage 206. Conversely when theactuation shaft 216 is retracted, the diaphragm 210 moves away from thevalve seat 208 thereby allowing flow through the passageway 206 therebyallowing flow through the passageway 206.

[0255] The movement of the shaft 216 is controlled by way of anelectrical induction coil 220 and spider bobbin 222 arrangement. In thepreferred embodiment, the electrical induction coil 220 is formedwithout having an internal support structure typically utilized ininduction coils so as to minimize inertial concerns. In this regard, thecoil 220 is typically formed by winding upon a mandrel and subsequentlymaintained in this wound configuration by way of application of asuitable binder or varnish. Additionally, in the preferred embodiment,the bobbin 222 is preferably formed having a cross-beam construction, asshown in FIG. 11b, to decrease the mass of the bobbin 222 whilemaintaining its structural integrity. Similarly, the shaft 216 ispreferably formed from a hollow stainless steel material so as to berelatively strong yet light weight enough for minimizing inertialconcerns.

[0256] As shown, the bobbin 222 is affixed to the distal end of theinduction coil 220 and the shaft 216 extends through an aperture formedin the center of the bobbin and is frictionally or otherwise affixed tothe bobbin such that the shaft 216 will move back and forth inaccordance with the bobbin 222 and coil 220. As the current passing intothe induction coil 220 increases, the coil 220 will translate rearwardlyinto the coil receiving space 226 about the magnet thereby moving theshaft 216 and blunt tip member 218 in the rearward direction andallowing the diaphragm 210 to move in an open position away from thevalve seat 208 of the expiratory flow path 206. With the diaphragm 210in such open position, expiratory flow from the patient PT may passthrough the expiratory flow pathway 206 and out the expiratory port 204.

[0257] Conversely, when the expiratory flow has decreased or terminated,the current into the induction coil may change direction, therebycausing the induction coil to translate forwardly. Such forwardtranslation of the induction coil 220 will drive the bobbin 222, shaft216, and bulbous tip member 218 in a forward direction, such that thebulbous tip member 218 will press against the flow distributing plate214 on the backside of the diaphragm 210 causing the diaphragm to seatagainst the valve seat 208. With the diaphragm 210 seated against thevalve seat 208, the inspiratory phase of the ventilator cycle may beginand ambient air will be prevented from aspirating or backflowing intothe patient circuit through the exhalation port 204.

[0258] In the preferred embodiment, a elastomeric boot 217 or dustbarrier is mounted about the distal portion of the hollow actuationshaft 216, and is configured and constructed to permit the shaft 216 tofreely move back and forth between its fully extended closed positionand a fully retracted open position while preventing dust or moisturefrom seeping or passing into the induction coil 220.

[0259] As best shown in FIG. 11, FIGS. 11a and 11 c, the housing of theexhalation valve 18 includes a frontal portion formed by the housingsegments 200 b, 200 c, and 200 d. An airway pressure passage 241 isprovided within the housing portion 200 b, which enables the pressurewithin the exhalation passageway 206 to be communicated to an airwaypressure tubing connector 233. Airway pressure tubing connector 233 isconnected via tubing to an airway pressure transducer 68 (shown in FIG.2) which monitors airway pressure and outputs a signal to the controller12. Based upon desired operating conditions, the controller 12, inresponse of receipt of the pressure signal from pressure transducer 68increases or decreases the voltage applied to the coil 220 to maintaindesired pressure within the exhalation air passage 206. As will berecognized, such monitoring of the airway pressure is continuous duringoperation of the ventilator cycle.

[0260] As previously mentioned, the exhalation flow transducer 230 ofthe present invention is preferably disposed with the exhalation valvehousing and serves to monitor exhalation flow from the patient PT. Moreparticular, the exhalation flow transducer 230 of the present inventionpreferably incorporates a feedback control system for providing realtime monitoring of the patient's actual expiratory flow rate. As bestshown in FIGS. 11a and 11 c, the expiratory flow transducer 230 of thepresent invention is incorporated within the exhalation flow path 206within housing segment 200 b. The flow transducer 230 is preferablyformed from a flat sheet of flexible material having a cut out region406 formed therein. A peripheral portion 408 of the flat sheet existsoutside of the cut out region 406 and flapper portion 231 is definedwithin the cut out region 406. Frame members 410 and 412 preferablyformed of a polymer material, are mounted on opposite sides of the flatsheet so as to exert inward clamping pressure on the peripheral portion408 of the flat sheet. The flapper portion 231 of the flat sheet is thusheld in its desired transverse position within the open central aperture14 a and 14 b of the transducer assembly, and such flapper portion 231is thus capable of flexing downstream in response to exhalation flow.

[0261] To minimize the inducement of stresses within the flow transducerassembly 230, a frame member 411 is preferably positioned in abuttingjuxtaposition to the outboard surface of at least one of the framemembers 410, 412. In the preferred embodiment shown in FIG. 11c, theframe member 411 is positioned in abutment with the upper frame member410. Such frame member 411 comprises a metal frame portion 413 andincludes an elastomeric cushioning gasket or washer 415 disposed on thelower side thereof. A central aperture 14 c is formed in the framemember 411, such aperture 14 c being of the same configuration, and inaxial alignment with central apertures 14 a, 14 b of the upper and lowerframe members 410, 412.

[0262] Upper and lower abutment shoulders 418 a, 418 b, are formedwithin the exhalation valve housing 200 to frictionally engage and holdthe flow transducer assembly 230 in its desired operative position. Whenso inserted, the upper engagement shoulder 418 a will abut against theupper surface of the frame member 411, and the lower abutment shoulder418 b will abut against the lower surface of the lower frame member 412,thereby exerting the desired inward compressive force on the flowtransducer assembly 230. As will be recognized, the inclusion of thecushioning washer 415 serves to evenly distribute clamping pressureabout the peripheral portion 408, thereby minimizing the creation oflocalized stress within the flow transducer 230.

[0263] When the transducer assembly 230 is operatively positionedbetween the upper and lower abutment shoulders 418 a, 418 b, an upstreampressure port 232 will be located upstream of the flapper 231, and adownstream pressure port 234 will be located downstream of the flapper231. By such arrangement, pressures may be concurrently measured throughupstream pressure port 232 and downstream pressure port 234 to determinethe difference in pressures upstream and downstream of the flapper 231.

[0264] As expiratory gas flow passes outwardly, through the outlet portof the exhalation valve 18, the flapper portion 231 of the flowtransducer 230 will deflect or move allowing such expiratory gas flow topass thereacross, but also creating a moderate flow restriction. Theflow restriction created by the flow transducer 230 results in apressure differential being developed across the flow transducer 230.Such pressure differential may be monitored by pressure ports 232 and234 disposed on opposite side of the flow transducer 230 (as shown inFIG. 11a) which pressure ports are in flow communication by internalpassages formed within the housing segment 200 c, 200 b and 200 a totubing connections 240 and 235. A manifold insert 201 may be mounted onthe upstream pressure port 232 such that the manifold insert 201protrudes into the expiratory flowpath 206, upstream of the flapper 231.A plurality of inlet apertures 201 a, preferably four in number areformed around the outer sidewall of the manifold insert 201, andcommunicate through a common central passageway with the upstreampressure port 232, thereby facilitating accurate measurement of thepressure within the expiratory flowpath 206 at that location.

[0265] An exhalation differential pressure transducer 70 (shown in FIG.2) may be located within the housing or enclosure of the ventilator 10.The exhalation differential pressure transducer 70 is connected by wayof tubing to the first and third pressure port tubing connectors 240 and235 so as to continuously measure and provide the controller 12 with thedifference between pressure upstream (P1) and pressure downstream (P2)of the flow transducer 230. The difference in pressure determined by theexhalation differential pressure transducer 70 is communicated to thecontroller, and the controller is operatively programmed to calculatethe actual flow rate at which expiratory gas is exiting the flow channel206. As will be recognized, the exhalation flow rate may be utilized bythe controller 12 for differing purposes such as triggering ofinitiation of the next inspiratory cycle.

[0266] Although the particular formation and mounting structure utilizedfor the exhalation flow transducer 230 provides exceptional accuracy inmost situations, the applicant has found that in certain circumstances,it is desirable to eliminate any inaccuracies caused by manufacturingand assembly tolerances. As such, in the preferred embodiment, thespecific operational characteristics of each exhalation flow transducer230, i.e., pressure differential for specific flow rates are measuredfor calibration purposes and stored on a storage medium contained withinthe exhalation valve housing 18. In the preferred embodiment thisspecific characterization and calibration information is encoded on aradio frequency transponder 203 of the type commercially available underthe product name Tiris, manufactured by Texas Instruments, of Austin,Tex. The radio-frequency transponder 203 and its associatedtransmitter/receiver antenna 203 a may be mounted within the exhalationvalve housing 200 as shown in FIG. 11c. Additionally, a radio frequencytransmitter/receiver is positioned within the ventilator system 10, suchthat upon command of the controller 12, the calibration andcharacterization data contained within the transponder 203 istransmitted via radio frequency to the receiver and stored within thecontroller 12. Subsequently, the controller 12 utilizes such storedcalibration and characterization data to specifically determineexpiratory flow rate based upon pressure differential values generatedby the differential pressure transducer 70.

F. A Preferred Auto Calibration Circuit

[0267] In the preferred embodiment, the ventilator device 14 of theventilator system 10 of the present invention incorporates an autocalibration circuit for periodic rezeroing of the system to avoid errorsin the tidal volume or inspiratory flow delivered by the drag compressor30.

[0268] In particular, as shown in FIG. 2 the preferred auto calibrationcircuit comprises the following components:

[0269] a) a first auto-zero valve 74 on the line between the inlet 32 ofthe compressor 30 and the differential pressure transducer 36;

[0270] b) a second auto-zero valve 76 on the line between the firstpressure port of the exhalation valve 18 and the first pressure (P1)side of the exhalation differential pressure transducer 70;

[0271] c) a third auto-zero valve 80 on the line between the secondpressure (P2) port 234 of the exhalation valve 18 and the secondpressure (P2) side of the exhalation differential pressure transducer70;

[0272] d) a fourth auto-zero valve 78 on the line between the outletport 34 and the differential pressure transducer 36; and

[0273] e) and a fifth auto-zero valve 72 on the line between the airwaypressure port 241 and the airway pressure transducer 68.

[0274] Each of the auto-zero valves 72, 74, 76, 78, 80 is connected tothe controller 12 such that, at selected time intervals during theventilatory cycle, the controller 12 may signal the auto-zero valves 72,74, 76, 78, 80 to open to atmospheric pressure. While the auto-zerovalve 72, 74, 76, 78, 80 are open to atmospheric pressure, thecontroller 12 may re-zero each of the transducers 36, 68, 70 to whichthe respective auto-zero valve 72, 74, 76, 80 are connected. Suchperiodic re-zeroing of the pressure transducers 36, 68 and 70 willcorrect any baseline (zero) drift which has occurred during operation.

Ventilator Operation

[0275] With the structure defined, the basic operation of the ventilatorsystem 10 of the present invention may be described. As will berecognized, the particular ventilatory mode selected by a technician maybe input to the controller 12 via the input controls upon, the display380. Additionally, the technician must attach the inspiratory andexhalation tubing circuit to the patient PT as illustrated in FIG. 1.

[0276] Prior to initiation of patient ventilation, the controller 12initiates its auto calibration circuit and system check to insure thatall system parameters are within operational specifications.Subsequently, inspiration is initiated wherein the controller 12 rapidlyaccelerates the drag compressor 30. During such acceleration, air isdrawn through the filter 50, accumulator 54 and supplied to the patientPT, via line 22. During such inspiratory phase, the controller 12monitors the pressure drop across the compressor 30, via pressuretransducer 36, and the rotational speed of the rotor 104. This data isthen converted to flow by the controller 12 via the turbinecharacterization table to insure that the proper flow and volume ofinspiratory gas is delivered to the patient PT. Additionally, duringsuch inspiratory phase, the exhalation valve 18 is maintained in aclosed position. In those applications where oxygen blending is desired,the controller 12 additionally opens selected ones of the solenoid valve52 a, 52 b, 52 c, 52 d and 52 e, in timed sequence to deliver a desiredvolume of oxygen to the accumulator 54, which is subsequently deliveredto the patient PT during inspiratory flow conditions.

[0277] When inspiratory flow is desired to be terminated, the controller12 rapidly stops or decelerates the drag compressor 30 to a basalrotational speed, and the patient is free to exhale through exhalationline 66 and through the exhalation valve 18. Depending upon desiredventilation mode operation, the controller 12 monitors the exhalationpressure, via pressure transducer 68 connected to the airway passage andadjusts the position of the valve relative the valve seat within theexhalation valve 18 to maintain desired airway pressures.Simultaneously, the controller 12 monitors the pressure differentialexisting across the exhalation flow transducer 230 via exhalationpressure transducer 70 to compute exhaled flow. This exhaled flow isused to compute exhaled volume and to determine a patient trigger. Whena breath is called for either through a machine or patient trigger, thecontroller initiates a subsequent inspiratory flow cycle with subsequentoperation of the ventilator system 10 being repeated between inspiratoryand exhalation cycles.

[0278] Those skilled in the art will recognize that differingventilation modes, such as intermittent mandatory ventilation (IMV),synchronized intermittent mandatory ventilation (SMIV) controlledmechanical ventilation (CMV) and assist control ventilation (A/C), areall available modes of operation on the ventilator 10 of the presentinvention. Further those skilled in the art will recognize that byproper selection of control inputs to the ventilator 10, all modernbreath types utilized in clinical practice, may be selected, such asmachine cycled mandatory breath, machine cycled assist breath, patientcycled supported breath, patient cycled spontaneous breath, volumecontrolled mandatory breaths, volume controlled assist breaths, pressurecontrolled breaths, pressure support breaths, sigh breaths, proportionalassist ventilation and volume assured pressure support.

What is claimed is:
 1. A rotary drag compressor ventilator device forventilating the lungs of a mammalian patient, said device comprising: A.a rotary drag compressor comprising: i. a housing having a gas inflowpassageway and a gas outflow passageway; ii. a rotor mounted within saidhousing, said rotor having a multiplicity of blades formed circularlytherearound such that, when said rotor is rotated in a first direction,said blades will compress gas within said housing and expel saidcompressed gas out of said outflow passageway; iii. a motor coupled tosaid compressor for rotating said rotor within said compressor housing;and B. a controller apparatus to intermittently accelerate anddecelerate the rotation of said rotor so as to deliver discrete periodsof inspiratory gas flow through said outflow passageway.
 2. Theventilator of claim 1, further in combination with: C. an oxygenblending apparatus connected to said inflow passageway for blendingoxygen with ambient air to provide oxygen-enriched air to the inletaperture of said compressor housing.
 3. The ventilator of claim 2wherein said oxygen blending apparatus comprises: an ambient airreceiving passageway; an oxygen receiving passageway; an accumulator forreceiving ambient air through said ambient air passageway and oxygenthrough said oxygen passageway; and, a series of independentlyactuatable solenoid valves positioned, in parallel, within the oxygenreceiving passageway of said bending apparatus, each of said solenoidvalves having a predetermined flow rate when fully open, each of saidsolenoid valves thereby permitting passage therethrough of apredetermined amount of oxygen per time period; and, said oxygenblending apparatus being connected to said controller and saidcontroller being further programmable to receive input of a desiredoxygen concentration setting and to emit control signals to the solenoidvalves to cause individual opening and closing of said solenoid valvesto result in said desired oxygen concentration within said accumulator.4. The ventilator system of claim 3 wherein said solenoid valvescomprises three to five separate solenoid valves.
 5. The ventilatorsystem of claim 3 wherein said controller is programmed to apply apulse-width modulation signal to control the opening and closing of saidsolenoid valves.
 6. The ventilator of claim 1 wherein said controllercomprises at least one microprocessor.
 7. The ventilator of claim 1wherein said compressor rotor comprises a dual-faced compressor rotorhaving first and second series of blades mounted opposite sides thereof;and, wherein said compressor housing is configured to define first andsecond compressor flow paths which are positioned in relation to saidfirst and second series of blades, respectively, such that rotation ofsaid compressor rotor in said first direction will a) draw gas into saidinflow passageway, b) concomitantly compress and move gas through bothof said first and second flow paths and, c) expel the combined gas fromsaid first and second compressor flow paths to compressor flow paths toprovide inspiratory gas flow from said ventilator device.
 8. Theventilator of claim 7 wherein said compressor rotor is round inconfiguration and has a diameter of 2-6 inches.
 9. The ventilator ofclaim 7 wherein said blades are disposed at angles of attack of 30-60degrees.
 10. The ventilator of claim 9 wherein said blades are disposedat 55° angles of attack.
 11. The compressor of claim 7 wherein saidblades are mounted within concave annular troughs formed on oppositesides of said dual-faced compressor rotor and wherein said first andsecond compressor flow paths are formed in relation to said first andsecond annular troughs such that the series of blades mounted within thefirst annular trough will compress gas within said first compressor flowpath and the series of blades mounted within said second trough willcompress gas within said second compressor flow path.
 12. The ventilatorof claim 7 wherein rotor, including said blades, had a mass of less than40 grams.
 13. The ventilator of claim 7 wherein said rotor furthercomprises: the convex rotor hub having a central transverse motor shaftreceiving aperture formed therein, to facilitate rotation of said rotorby said motor.
 14. The ventilator of claim 7 wherein said rotor isformed of molded material.
 15. The ventilator of claim 7 wherein saidblades are formed of aluminum.
 16. The ventilator of claim 7 whereinapproximately 30-40 blades are positioned on either side of said rotor.17. The ventilator of claim 1 further comprising: a differentialpressure transducer for measuring the difference in pressure between gasentering the inlet of said compressor and gas exiting the outlet of saidcompressor.
 18. The ventilator of claim 1 further comprising: atachometer for measuring the rotational speed of said compressor. 19.The ventilator of claim 18 wherein said tachometer comprises an opticalencoder.
 20. The ventilator of claim 1 further comprising: adifferential pressure transducer for measuring the difference inpressure between gas entering the inlet of said compressor and gasentering the outlet of said compressor; a tachometer for measuring therotational speed of said compressor; and said differential pressuretransducer and said tachometer being in communication with saidcontroller; and said controller being programmed to determine theinstantaneous flow rate and current accumulated volume of inspiratorygas flow delivered by said ventilator based on the pressure differentialmeasured by said differential pressure transducer and the rotationalspeed measured by said tachometer.
 21. The ventilator of claim 1 whereinsaid compressor incorporates a controller-readable data base containingspecific rotational speed, differential pressure and flow rate data forthat particular compressor; and wherein said controller is furtherprogrammed to read said data base and to utilize information obtainedfrom said data base in the calculation of inspiratory flow, volume orpressure delivered by said ventilator.
 22. The ventilator of claim 21wherein said controller-readable data base comprises an EPROM.
 23. Theventilator of claim 1 further in combination with a portable battery forsupplying power to said device.
 24. The ventilator of claim 23 whereinsaid portable battery contains sufficient power to operate saidmechanical ventilator device for at least two hours.
 25. A dragcompressor apparatus for creating inspiratory gas flow in a mechanicalventilator, said compressor apparatus comprising: a housing having a gasinflow passageway and a gas outflow passageway; a rotor rotatablymounted within said housing, said rotor being configured and constructedsuch that rotation of said rotor in a first direction will cause saidrotor to a) draw gas in said inflow passageway, b) compress said gas andc) expel said gas out of said outflow passageway; a controller forcontrolling the rotation of said rotor within said housing, saidcontroller being operative to cause said rotor to intermittentlyaccelerate and decelerate so as to deliver discrete periods ofinspiratory gas flow through said outflow passageway.
 26. The compressorof claim 25 wherein said rotor incorporates at least one series ofblades having leading edges, each of said blades being disposed at apositive angle of attack such that, when said rotor is rotated in saidfirst direction, the leading edge of each blade will precede theremainder thereof.
 27. The compressor of claim 26 wherein said bladesare disposed at angles of attack of 30-60 degrees.
 28. The compressor ofclaim 27 wherein said blades are disposed at 55 degree angles of attack.29. The compressor of claim 26 wherein said blades are disposed atspaced intervals within an annular trough which extends about said rotorsuch that, when said rotor is rotating said first direction, said bladeswill serially contact and compress gas within said housing.
 30. Thecompressor of claim 29 wherein said housing is further configured todefine therewithin at least one compressor flow path said flow pathbeing positioned in relation to said annular trough and being connectedto said inflow and outflow passageways such that, when said rotor isrotated in said first direction, the blades of said rotor will a) drawgas inwardly through said inflow passageway into said compressor flowpath, b) compress said gas within said compressor flow path, and c)expel said gas out of said outflow passageway.
 31. The compressor ofclaim 31 wherein each of said blades has a leading edge and at least oneperipheral edge, and wherein said blades are mounted within said troughsuch that the leading edges of the blades extend transversely across thetrough and the peripheral edge of said blades are in abutment with saidtrough.
 32. The compressor of claim 30 wherein said at least one concaveannular trough comprises: a first annular trough which extends about theperiphery of said rotor on a first side thereof; and, a second annulartrough which extends about the periphery of said rotor on a second sidethereof.
 33. The compressor of claim 32 wherein said housing isconfigured to define therewithin: a first compressor flow path which isat least partially within said first annular trough and is connected tosaid inflow passageway and said outflow passageway; and, a secondcompressor flow path which is at least partially within said secondannular trough and is connected to said inflow passageway and saidoutflow passageway; said first and second compressor flow paths beingconfigured and positioned such that, when said rotor is rotated in saidfirst direction, the blades mounted within said first annular troughwill draw gas into said inflow passageway, compress said gas within saidfirst flow path, and expel said gas out of said outflow passageway andthe blades mounted within said second annular trough will draw gas intosaid inflow passageway, compress sid gas within said second flow path,and expel said gas out of said outflow passageway.
 34. The compressor ofclaim 33 wherein said first concave trough and the blades mountedtherewithin are mirror images of said second concave trough and theblades mounted therewithin.
 35. The compressor of claim 25 furthercomprising a drive motor located within said compressor housing andcoupled to said rotor to rotatably drive said rotor.
 36. The compressorof claim 25 wherein said housing further comprises a number of heatdissipation fins formed on the outside of the portion of said housingwherein said motor is positioned to facilitate dissipation of heat fromsaid motor.
 37. The compressor of claim 35 further comprising atachometer for measuring the rotational speed of said rotor.
 38. Thecompressor of claim 37 wherein said tachometer comprises an opticalencoder.
 40. The compressor of claim 25 further comprising: adifferential pressure transducer for measuring the difference betweenthe pressure of gas in said inflow passageway and the pressure of gas insaid outflow passageway.
 41. An exhalation valve for controlling theexpiratory gas flow from a mammalian patient, said exhalation valvecomprising: a housing defining an expiratory gas flow passagewaytherethrough; a valve seat formed within said expiratory gas flowpassageway; an annular diaphragm movably disposed within said gas flowpassageway, in juxtaposition to said valve seat, said diaphragm beingvariably movable back and forth to various positions between andincluding: i) a fully closed position wherein said diaphragm is firmlyseated against said valve seat to prevent gas from flowing through saidpassageway; and ii) a fully open position wherein said diaphragm isretracted away from said annular valve seat so as to permitsubstantially unrestricted flow of expiratory gas through said pathway;an elongate actuation shaft having a proximal end and a distal end, thedistal end of said actuation shaft being contractable with saiddiaphragm, and said actuation shaft being axially moveable back andforth to control the positioning of said diaphragm between said fullyclosed and said fully open positions; an electrical induction coillinked to said actuation shaft such that a decrease in the currentpassing into said induction coil will cause said shaft to advance in thedistal direction and an increase in the current passing into saidinduction coil will cause said shaft to retract in the proximaldirection; means for determining the flow rate of expiratory gas passingout of said exhalation valve; means for determining airway pressure; amicroprocessor controller connected to said means for determining airwaypressure, said controller being provided with a positive expiratorypressure setting, and said controller being connected to said inductioncoil and adapted to emit control signals to said induction coil tocontrol the movement of said actuation shaft in response to the currentairway pressure, thereby maintaining the present amount of positiveexpiratory pressure; a radio frequency transponder database containingflow characterization data for the means for determining the flow rateof expiratory gas passing out of said exhalation valve; said controllerbeing further connected to said means for determining the flow rate ofexpiratory gas passing out of said exhalation valve and being equippedto receive radio frequency input of the characterization data containedin the radio frequency transponder database, and to utilize such data todetermine the instant flow rate of expiratory gas passing out of saidexhalation valve.
 43. The exhalation valve of claim 42 wherein saidcontroller is located separately from, said exhalation valve.
 44. Theexhalation valve of claim 41 wherein said controller is further adaptedto receive input signals from said means for determining the flow rateat which expiratory gas is passing outwardly through said expiratory gasflow passageway, and for emitting control signals to said induction coilto fully close said diaphragm when said flow rate has fallen to apredetermined basal level, thus signifying the end of the expiratoryphase.
 45. A method of providing pulmonary ventilation to a mammalianpatient, said method comprising the steps of: a) providing a rotary dragcompressor device comprising: i) a housing having an inflow passagewayand an outflow passageway formed therein; and, ii) a rotor rotatablymounted within said housing such that rotation of said rotor in a firstdirection will draw gas into said inflow passageway, compress said gas,and expel said gas out of said outflow passageway; b) connecting theoutflow passageway of said rotary drag compressor to a conduit throughwhich respiratory gas flow may be passed into the patient's lungs; c)accelerating said rotor to a first rotational speed for sufficient timeto deliver a desired inspiratory gas flow through said conduit and intothe patient's lungs; d) stopping said rotor or decelerating said rotorto a basal rotational speed to terminate the inspiratory gas flowthrough said conduit and to allow the expiratory phase of theventilation cycle to occur.
 46. The method of claim 45 wherein step bcomprises connecting said overflow passageway to an endotracheal tubeinserted into the trachea of the patient.
 47. The method of claim 45wherein step b comprises connecting said outflow passageway to anasotracheal tube inserted into the trachea of the patient.
 48. Themethod of claim 45 wherein step b comprises connecting said outflowpassageway to a tracheostomy tube inserted into the trachea of thepatient.
 49. The method of claim 45 wherein step b comprises connectingsaid outflow passageway to a mask which is positioned over the nose andmouth of the patient.
 50. The method of claim 45 wherein step c iscommenced upon the occurrence of a triggering event, said triggeringevent being selected from the group of triggering events consisting of:i) the passing of a predetermined time period; and ii) the initiation ofspontaneous inspiratory effort by the patient.
 51. The method of claim45 wherein the inspiratory gas flow delivered in step c is limited by alimiting parameter selected from the group of limiting parametersconsisting of: i. a predetermined minimum airway pressure; ii. apredetermined maximum airway pressure; iii. a predetermined minimum flowrate; iv. a predetermined maximum flow rate; v. a predetermined minimumtidal volume; and vi. a predetermined maximum tidal volume.
 52. Themethod of claim 45 wherein step c is terminated and step d is commencedupon the occurrence of a selected terminating event, said terminatingevent being selected from the group of terminating events consisting of:i. the passing of a predetermined period of time since the commencementof step c; ii. the attainment of a predetermined airway pressure; andiii. the passage of a predetermined tidal volume of inspiratory gas. 53.The method of claim 45 wherein step c further comprises controlling thespeed to which said rotor is accelerated during the inspiratory phaseby: i. storing specific rotor speed, compressor differential pressureand flow rate characterization data for the compressor; ii. providing afirst input signal to said compressor which is intended to cause therotor to rotate at a speed calculated to deliver a desired flow rate;iii. determining the actual flow rate generated by said compressor inresponse to said first input signal; iv. comparing the actual flow ratedetermined in step iii, to the desired flow rate; v. adjusting the inputsignal to said compressor to provide the desired flow rate.
 54. Themethod of claim 53 wherein step c further comprises: vi. repeating stepsii-v, as necessary to achieve said desired flow rate.
 55. A rotary dragcompressor ventilator device for delivering inspiratory gas flow to amammalian patient, said device comprising: a) a rotary drag compressorhaving an intake port and an outflow port; b) an inspiratory gas flowpassageway for carrying gas from the outflow port of the compressor tothe patient during the inspiratory phase of the ventilation cycle; c)means for accelerating said compressor at the beginning of theinspiratory phase of the ventilation cycle to deliver inspiratory gasflow through said passageway to said patient; d) means for controllingsaid compressor during the inspiratory phase of the ventilation cycle tomaintain a desired inspiratory pressure and flow rate; and, e) means fordecelerating said compressor at the end of the inspiratory phase of theventilation cycle.
 56. The ventilator device of claim 55 wherein saidinspiratory gas flow passageway is devoid of valves for diverting theinspiratory gas flow away from said patient.
 57. The ventilator deviceof claim 55 wherein said rotary drag compressor comprises: a compressorhousing having said intake and outflow ports formed therein; a rotormounted within said housing such that rotation of said rotor in a firstdirection will cause said inspiratory gas flow to be delivered out ofsaid outflow port and through said inspiratory gas flow passageway tosaid patient; and, a motor for rotating said rotor within said housing.58. The ventilator device of claim 55 wherein said means foraccelerating, controlling and decelerating said compressor comprise: amicroprocessor controller connected to said compressor.
 59. Theventilator device of claim 55 further comprising: f) an exhalationconduit for carrying expiratory gas flow from said patient during theexpiratory phase of the ventilation cycle; g) an exhalation valvepositioned on said exhalation conduit, said exhalation valve beingconstructed to: i) open during the expiratory phase of the ventilationcycle to permit the expiratory gas flow to pass out of said exhalationconduit, and ii) close during the inspiratory phase of the ventilationcycle to prevent gas from being drawn into said patient through saidexhalation conduit.
 60. The ventilator device of claim 55 furthercomprising: f) an oxygen blending apparatus connected to said intakeport to provide oxygen-enriched air to said compressor.
 61. Anexhalation valve comprising: a) a housing defining a first exhalationpassageway through which expiratory gas may outflow in a firstdirection; b) a valve seat formed within said passageway; c) a diaphragmhaving a front side and a back side, said diaphragm being sized andconfigured such that the front side thereof may abut against said valveseat valve seat to thereby block the flow of gas through said exhalationpassageway, said diaphragm being moveable back and forth between; i) afirst position wherein said diaphragm is fully retracted from said valveseat to permit unrestricted flow through said passageway; ii) a secondposition wherein said diaphragm is seated on said valve seat to blockflow through said passageway; iii) a range of intermediate positionsbetween said first and second positions wherein said diaphragm willcause varying degrees of restriction of the flow through saidpassageway; d) an elongate shaft having a first end and a second end,the first end of said shaft being adjacent to the back side of saiddiaphragm, said shaft being axially moveable back and forth between; i)a first position wherein the first end of said shaft is at a locationwhich will retain said diaphragm in its first position; ii) a secondposition wherein the first and of said shaft is at a location which willallow said diaphragm to move to its second position; and, iii) a rangeof intermediate positions wherein said shaft is at a location which willallow said diaphragm to move to one of its intermediate positions; e) anelectrical induction coil slidably mounted within said housing so as tomove back and forth in response to changes in current applied to thecoil, said coil consisting essentially of multiple convolutions of wireupon which a rigidifying coating has been applied to hold said wire in aclosely coiled substantially cylindrical configuration; f) a mountingspider connecting said shaft to said coil, said spider configured tohold said shaft in co-axial alignment with the longitudinal axis of thecoil, with the first end of the shaft protruding toward the back side ofsaid diaphragm such that, when the coil moves forward, said shaft willmove forward toward said first shaft position, and when said coil movesrearward, said shaft will be retracted toward said second shaftposition.
 62. The exhalation valve of claim 61 wherein the front surfaceof said diaphragm is planar and wherein said valve seat is angledrelative to the plane of the front surface of the diaphragm such that,when said diaphragm is moving into said first diaphragm position, thefront side of said diaphragm will initially contact only one side ofsaid diaphragm and will subsequently move into contact with theremainder of said valve seat.
 63. The exhalation valve of claim 61further comprising: g) a pliable dust barrier disposed between saidvalve seat and said induction coil, said pliable dust barrier beingsealed to the surrounding housing to prevent particulate matter frompassing around said shaft and into said induction coil, said dustbarrier being in contact with said shaft and being sufficiently flexibleto move back and forth in accordance with axial movement of said shaft.64. The exhalation valve of claim 63 wherein said dust barrier comprisesan elastomeric boot.
 65. The exhalation valve of claim 63 wherein atleast one vent hole is formed in said exhalation valve to prevent thecreation of pressure on at least one side of said dust barrier as saiddust barrier flexes back and forth.
 66. An exhalation valve comprising:a) a housing defining an expiratory gas flow path connectable to amammalian patient such that expiratory gas exhaled by the patient willpass through said flow path in a first direction; b) a valve associatedwith said flow path to permit gas exhaled by the patient to pass throughsaid flow path in said first direction, but to prevent gas from beingdrawn through said flow path, in a second direction opposite said firstdirection, when said patient inhales; c) a flow measuring apparatus formonitoring the flow rate of expiratory gas passing through saidexhalation valve.
 67. The exhalation valve of claim 66 wherein said flowmeasuring apparatus comprises: a flapper disposed transversely withinsaid flow path, said flapper being constructed such that at least aportion of said flapper will deflect in a first direction when exhaledgas is passed through said flow path in said first direction, the extentof flapper deflection being variable with the flow rate of gas passingthrough the exhalation valve, said flapper thereby creating a dynamicflow restricting orifice within said flow path; means for determininggas pressure within said flow path upstream of said flapper; means fordetermining gas pressure within said flow path downstream of saidflapper; and means for determining the then-current flow rate of gaspassing through said exhalation valve, based on the difference in thepressures measured upstream and downstream of said flapper.
 68. Theexhalation valve device of claim 72 wherein said flapper is mountedwithin a flapper assembly which comprises: a sheet of pliable materialhaving a first side, a second side and an outer peripheral edge, asemi-annular cut being formed in said sheet to divide said sheet into i)an outer peripheral portion which is outboard of said cut and ii) aninner flapper portion which is inboard of said cut, and which remainsattached on one side thereof to the surrounding peripheral portion ofsaid sheet, said inner flapper portion of said sheet being therebydeflectable back and forth while the outer peripheral portion of saidsheet is held in substantially stationary position; a first frame memberhaving a central aperture formed therein, said first frame member beingjuxtaposed to the first side of said sheet such that said first framemember is in contact with the first side of the peripheral portion ofsaid sheet such that said first frame member is in abutment with thefirst side of the peripheral portion of said sheet and the centralaperture of said first frame member surrounds the first side of theflapper portion of said sheet; a second frame member having a centralaperture formed therein, said second frame member being juxtaposed tothe second side of said sheet such that said frame member abuts againstthe second side of the peripheral portion of said sheet, and the centralaperture of said second frame member surrounds the second side of theflapper portion of said sheet; said first and second frame membersthereby holding the peripheral portion of said sheet in a substantiallyfixed position between said frame members while the flapper portion ofsaid sheet extends transversely into the space between the axiallyaligned apertures of said frame members and is deflectable back andforth therein.
 69. The exhalation valve device of claim 68 wherein saidflapper assembly is positioned transversely within the flow path of saidexhalation valve and is held in such position by engagement to thesurrounding exhalation valve housing.
 70. The exhalation valve device ofclaim 66 further comprising: specific flow-pressure calibrationinformation for the flow measuring apparatus stored on a storage mediumcontained within the exhalation valve housing.
 71. The exhalation valvedevice of claim 70 wherein said storage medium comprises aradio-frequency transponder.
 72. The exhalation valve device of claim 70wherein the characterization information stored on said storage mediumcomprises a data base of predetermined pressure differences for specificflow rates of exhalation valve.
 73. The exhalation valve device of claim70 wherein the information stored on said storage medium comprises anequation for calculating specific flow rates based on measured pressuredifferentials for that exhalation valve.
 74. The exhalation valve deviceof claim 68 further comprising: a cushioning washer and a third framemember disposed on at least one of the first and second frame memberswhich abut against the same so as to evenly distribute stresses appliedto said sheet by said frame members.
 75. The exhalation valve device ofclaim 74 wherein said cushioning washer comprises an elastomericmaterial disposed on said third frame member.
 76. An oxygen blendingapparatus for delivering oxygen enriched air to a ventilator, saidapparatus comprising: a) an accumulator chamber; b) an air inlet conduitconnected to said accumulator chamber; c) an oxygen inlet conduitconnected to said accumulator chamber; d) a series of solenoid valvesconnected, in parallel, within said oxygen inlet conduit, each of saidsolenoid valves having a predetermined orifice size; and e) a controllerfor independently opening and closing each of the solenoid valves tocontrol the amount of oxygen which flows into the accumulator chamberduring a time period.
 77. The oxygen blending apparatus of claim 76further in combination with a ventilator device connected to the outletof said accumulator chamber, said ventilator device being operative tointermittently draw inspiratory gas from said accumulator chamber tocompress and expel said gas to provide an inspiratory flow.
 78. Theoxygen blending apparatus of claim 77 wherein said controller is furtherprogrammed to repeatedly determine the volume of oxygen enriched gaswhich has been drawn from the accumulator chamber during thethen-current inspiratory phase, and to subsequently adjust the openingand closing of the solenoid valves to maintain the prescribed oxygenconcentration of gas drawn from the accumulator chamber during thereminder of that inspiratory phase.
 79. The oxygen blending apparatus ofclaim 78 wherein said controller is further programmed to repeatedlycompare the then-current accumulated volume of oxygen enriched gas to apredetermined trigger volume for each of the solenoid valves, and toopen each solenoid valve for a predetermined period of time when it isdetermined that the accumulated volume of oxygen-enriched air hasexceeded the trigger volume for that individual solenoid valve.
 80. Theoxygen blending apparatus of claim 76 wherein said solenoid valvescomprise at least first, second, third and fourth solenoid valves, andwherein a predetermined oxygen pressure is constantly passed into saidoxygen inlet conduit.
 81. The oxygen blending apparatus of claim 80wherein said first, second, third, and fourth solenoid valves have flowrates, at a predetermined oxygen inlet operating pressure, of 5liters/min., 14.7 liters/min.; 40 liters/min. and 80 liters/min.,respectively.
 82. The oxygen blending apparatus of claim 76 wherein theventilator device connected to the outlet of the accumulator chambercomprises the ventilator device of claim
 55. 83. The oxygen blendingapparatus of claim 82 wherein the controller which controls opening andclosing of the solenoid valves is incorporated into the means forcontrolling the ventilator compressor.
 84. A flow transducer formeasuring the flow rate of a fluid, said transducer comprising: ahousing defining a first fluid flow path therethrough; a deflectableflapper disposed transversely within said fluid flow path such that saidflapper will deflect in the direction of fluid flow, thereby creating afluid flow restriction permitting some fluid to flow past said flapperand through said flow path; a first pressure port located upstream ofsaid flapper for measuring the pressure of fluid within said flow path,upstream of said flapper; a second pressure port downstream of saidflapper for measuring the pressure of fluid flowing through said flowpath, downstream of said flapper; means associated with first pressureport for determining the pressure of fluid flowing upstream of saidflapper; means associated with said second pressure port for determiningthe pressure of fluid flowing downstream of said flapper; means fordetermining the difference between the pressure of fluid flowingupstream of said flapper and the pressure of fluid flowing downstream ofsaid flapper; and means for computing the flow rate of fluid throughsaid flow path, based on the measured difference in pressures upstreamand downstream of said flapper.
 85. The fluid flow transducer of claim84, wherein said deflectable flapper comprises: a rigid frame having acentral aperture formed therein; a flat sheet of pliable materialmounted within said frame member and forming a flapper disposedtransversely within the central aperture of said frame and deflectablein at least one direction to permit fluid to flow past said flapper andthrough said central aperture; said frame being mounted transverselywithin said flow path such that fluid flowing in a first directionthrough said flow path will strike said flapper, thereby causing saidflapper to deflect in the direction of flow such that the flowing fluidmay pass through said central aperture.
 86. The flow transducer of claim85 wherein: said flat sheet of pliable material comprises an outerperipheral portion, an inner flapper portion, and a semi-annular cutformed in said sheet to free most of said peripheral portion from saidflapper portion; and said rigid frame comprises first and second framemembers disposed on opposite sides of the peripheral portion of saidflat sheet, said frame members being compressed inwardly tocompressively hold said peripheral portion of said flat sheet betweensaid frame members such that the flapper portion of said flat sheet istransversely disposed and deflectable within the central aperture ofsaid frame.
 87. The flow transducer of claim 84 further comprising: acushioning member associated with said flapper to distribute the forceexerted on said flapper thereby distributing any stresses created withinsaid flapper.
 88. The flow transducer of claim 85 further comprising: acushioning member associated with said frame to distribute the forceexerted by said frame on said flat sheet of pliable material, therebydistributing any stresses of created within said flat sheet of pliablematerial.
 89. The flow transducer of claim 84 wherein said housingcomprises a portion of an exhalation valve through which a mammalianpatient is permitted to exhale, said flow transducer being disposedwithin said exhaltion valve to measure the flow rate of expiratory gaspassing through said exhalation valve.
 90. The flow transducer of claim84 further comprising: a deflector member positioned on at least one ofsaid first and second pressure ports to deter fluid from being forceddirectly into the pressure port on which deflector insert is positioned.91. The flow transducer of claim 84 wherein said means for computingflow rate comprises a microprocessor.
 92. The flow transducer of claim86 wherein: said housing incorporates first and second abutment ridgesformed about-said flow path; said first and second frame members, havingsaid flat sheet of pliable material therebetween, being positionedbetween said abutment ridges such that said abutment ridges will exertinward compressive force on said first and second frame members tocompressively hold said flat sheet therebetween.
 93. The flow transducerof claim 84 further comprising: specific flow-pressure calibrationinformation for the flow transducer stored on a storage medium containedwithin said housing.
 94. The flow transducer of claim 93 wherein saidstorage medium comprises a radio-frequency transponder.
 95. The flowtransducer of claim 93 wherein the specific flow-pressure calibrationinformation stored on said storage medium comprises a data base ofpredetermined pressure differences for specific flow rates of fluidthrough said flow path.
 96. The flow transducer of claim 93 wherein thecalibration information stored on said storage medium comprises anequation for calculating specific flow rates based on measureddifferences in pressure upstream and downstream of said flapper.